J. Nannoplankton Res., 39(1), 2021, pp. 29–75 © 2021 International Nannoplankton Association
ISSN 1210-8049 Printed by The Sheridan Press, USA

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Ultrastructure and taxonomy of the family Sphenolithaceae
Richard Howe
Ellington Geological Services, 1414 Lumpkin Road, Houston, TX 77043, USA; richard.howe@ellingtongeo.com
Manuscript received 21st August, 2020; revised manuscript accepted 26th March, 2021

Abstract Coccolith species belonging to the family Sphenolithaceae, in the genera Sphenolithus and Furcatolithus, are widespread and common throughout most of the Cenozoic. This study details their ultrastructure, emphasising the importance of recognising their major structural components. In Sphenolithus, these are: 1) the proximal
element cycle; 2) the lower lateral element cycle; 3) the upper lateral element cycle; and 4) the apical structure. In
Furcatolithus, these are: 1) the proximal element cycle; and 2) the bifid spine, which is derived from the upper lateralelement cycle in Sphenolithus. The evolutionary transition from Sphenolithus to Furcatolithus involved loss of thelower lateral element cycle and the apical structure, and upward growth of the upper lateral element cycle into thebifid spine. Here, 65 species are recognised as valid within the Sphenolithaceae (48 in Sphenolithus and 17 in Furcatolithus) and are described in detail. Two new species––Sphenolithus shamrockiae n. sp. and S. bergenii n. sp––areintroduced. The family Sphenolithaceae, the genera Sphenolithus and Furcatolithus and the species S. furcatolithoides
and S. delphix are emended. Sixteen species previously assigned to Sphenolithus are recombined into Furcatolithus––F. akropodus, F. avis, F. bulbulus, F. celsus, F. ciperoensis, F. cuniculus, F. directus, F. intercalaris, F. obtusus, F.
patifunditis, F. peartiae, F. predistentus, F. tawfikii, F. triangularis, F. tribulosus and F. umbrellus.

Keywords nannofossils, coccoliths, Discoasterales, Sphenolithaceae, Sphenolithus, Furcatolithus, Cenozoic,
Neogene, Palaeogene, taxonomy, ultrastructure

1. Introduction
The family Sphenolithaceae is a group of Cenozoic calcareous nannofossils that originated in the Late Paleocene(Late Danian) and flourished until the end of the Early
Pliocene (Zanclean). They are one of the most importantgroups used in Cenozoic nannofossil biostratigraphy, butdifferentiating among species is often difficult because
many species share the same basic structure, but withvarying proportions of the major components. The twogenera included in the Sphenolithaceae––Sphenolithus
and Furcatolithus––are clearly related; however, there aremajor ultrastructural differences between them that havenot been fully recognised in previous studies.
This study arose from the realisation that the upperand lower lateral element cycles present in Sphenolithus
coccoliths have been conserved throughout the geological history of the genus, and hence are fundamentally
important characteristics for discriminating between species. Previous studies have tended to consider the lateralelement cycles in two fundamentally different ways: 1) aspart of the base of the coccolith (e.g. the upper pair of thefour basal quadrants of Young et al., 1997); or 2) as part ofFour distinct ultrastructural components of Sphenolithus species were distinguished in this study (Figures
1–4): 1) the proximal element cycle; 2) the lower lateralelement cycle; 3) the upper lateral element cycle; and 4)
the apical structure. The characterisation and subsequent
recognition of Sphenolithus species requires that all fourof these components are described fully. In this study, allpreviously described species of Sphenolithus were considered, as well as those ascribed to other genera considered to belong to the Sphenolithaceae. The taxonomy was
rationalised, and all valid species were described using acommon ultrastructural framework and terminology.
Once the importance of the lateral element cycles in
Sphenolithus species was understood, it was further recognised that, in the lineage that arose with Sphenolithus
kempii, the upper lateral element cycle underwent a seriesof modifications through time. The upper lateral element
cycle in species of this lineage increased in height vertically over time, with the number of elements in the cycle
being reduced, ultimately to two. Concurrently, the apicalstructure diminished and eventually disappeared.
The modified upper lateral element cycle became athe upper part of the coccolith (e.g. the lower part of thecalyptra of Aubry, 2014). In both instances, the resulting
two-part ultrastructural division minimises the importanceof the lateral element cycles.

vertically split, two-part spine, here termed the bifid spine(Figures 1H–K, 3B, 4), with a very different appearance tothe upper lateral element cycle it was derived from. With
subsequent loss of the lower lateral element cycle, the lin-

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Figure 1: Schematic sketches showing the ultrastructural components of sphenolithid species and variations in their proportions. For each sketch, an
example of a species showing the same characteristics is listed. Only elements with the long axes parallel to the plane of the slide are shownUltrastructure and taxonomy of the Sphenolithaceae

eage that resulted has clear structural differences from theSphenolithus species it descended from. Species in thisdiverged lineage were recombined here into the emended
genus Furcatolithus. In clear contrast to the four distinct
ultrastructural components in Sphenolithus, species in
Furcatolithus only have two.
2. Origin of the familySpecies in the family Sphenolithaceae are consideredhere to be heterococcoliths in the order Discoasterales.
They are constructed of vertically stacked cycles of radially oriented elements, with radial c-axes in each element.
Aubry (2014) indicated that the earliest known species in
the Sphenolithaceae descended from the Danian genus Diantholitha Aubry in Aubry et al. (2011), based on strong
similarities in the proximal element cycles of Diantholitha
and early specimens of Sphenolithus primus. Above theproximal cycle, Diantholitha has a single distal cycle ofelements, in contrast to the multiple element cycles in S.

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primus.
The addition of extra cycles of elements above the distal cycle in Diantholitha is a plausible step in the transition between the two genera. Aubry (2014) considered
Diantholitha to be descended from the Early Danian genus
Biantholithus, which has well-documented occurrences ofintact coccospheres (Mai, 2001), and is clearly a coccolithophorid. Speculation by Towe (1979, fig. 8) and Aubry(2014, text-fig. 27a, b) that Sphenolithus and Furcatolithus
form coccospheres, with the concave (proximal) surfaceof the coccoliths being situated adjacent to the living cell,is certainly plausible, although there is little evidence tosupport the interpretation by Towe (1979, p. 569) that thecoccoliths on these coccospheres were polymorphic.
3. Morphology and ultrastructure
Species in the Sphenolithaceae show a range of grossmorphologies that are all roughly cylindrical, in contrast
to most heterococcoliths, which are approximately disc-

Figure 2: Schematic sketches (based on holotype specimens) showing the major ultrastructural components of (A) S. abies and(B) S. pseudoradians. Only elements with the long axes parallel to the plane of the slide are shown

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Figure 3: Schematic sketches (based on holotype specimens) showing the major ultrastructural components of (A) S. heteromorphus and(B) F. ciperoensis. Only elements with the long axes parallel to the plane of the slide are shown

shaped. Although, without preserved coccospheres, wecannot be sure of the original orientation of such cylindrical coccoliths, the generally broader, concave end is assumed to be the proximal end, with the opposite end assumed to be the distal end. The distal surface of coccoliths
in the Sphenolithaceae may be rounded, flat or spinose,
conical or flaring, and may bifurcate or be spinose. The
basal surface is always concave, above which there is one
or more stacked cycles of lath-shaped elements, arranged
radially around the median axis of the coccolith. The basal
cycle, termed the proximal cycle, is similar in all members of the Sphenolithaceae, reflecting their common origin (Figures 1–4). The upper central point of the proximal
cycle, on the median axis, is termed the core (Young et al.,1997), and is the point from which all of the elements inthe coccolith radiate (Figures 1–4).
Coccoliths belonging to the genus Sphenolithus are
termed sphenoliths. Above the proximal cycle, species inthis genus have two vertically stacked element cycles––the lower and upper lateral cycles (Figures 1A–G, 2, 3A,
4). Previously, this term has been used for all members of
the family, but here it is strictly limited to species that haveboth lower and upper lateral element cycles and belong to
the genus Sphenolithus.
Above the upper lateral element cycle in most sphenoliths, there is an apical structure, which may comprisea single vertical or sub-vertical element, termed a monocrystalline apical structure (Figures 1E–G, 3A), or single
or multiple cycles of elements, termed monocyclic (Figure1D) or polycyclic (Figures 1A–C, 2A) composite apicalstructures, respectively. Some sphenoliths completely lackany apical structure (e.g. S. labradorensis, Plate 2, figs
7–10).
Species in the Sphenolithaceae that lack a lower lateral element cycle belong to the genus Furcatolithus (Figures 1J–L, 3B, 4). All species in this genus lack any apical structure. Coccoliths of these species are here referred
to as furcatoliths. The presence or absence of the lower

Ultrastructure and taxonomy of the Sphenolithaceae

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Figure 4: Schematic sketches of a range of sphenoliths and furcatoliths (based on holotype or paratype specimens) showing the major ultrastructuralcomponents. Only elements with the long axes parallel to the plane of the slide are shown

lateral cycle is the major structural difference between
Sphenolithus and Furcatolithus, and is used here as theprimary criterion for separating them (Figure 4). In somesphenoliths and all furcatoliths (except the last furcatolith
species, F. umbrellus, which usually lacks any structure
above the proximal cycle), the upper lateral element cycle
is present, but is reduced to two elements, and is greatly
enlarged vertically, forming a bifurcated distal spine. This
spine is here termed the bifid spine (Figures 1H–K, 3B, 4).
The structural components of sphenoliths and furcatoliths
are discussed in detail below.
3.1 Element shape and arrangement
In electron microscope (EM) images of well-preserved
specimens of many sphenolith species, it is evident thatthe individual elements are elongated, triradiate laths, withthree blades extending at varying angles to the long axisof the elements, resulting in a ‘Y’ shape in cross-section(Figure 5). The intersection of the blades is here termed
the blade axis. The three blades of each element share asingle c-axis orientation, suggesting that the blades are
all part of a single crystal of calcite. Individual elements
showing this triradiate morphology were termed triades

by Aubry (2014). The fact that early Sphenolithus species(e.g. specimens of Sphenolithus primus in Bybell & SelfTrail, 1997, pl. 5, fig. 8) and one of the last surviving species (e.g. specimens of S. abies in Figure 5, and in PerchNielsen, 1972, pl. 17, fig. 6) both possess similar-shaped
triradiate elements demonstrates that this ultrastructure
has been conserved throughout the history of the genus,
particularly in species belonging to the long-ranging S.
primus group, from which all other groups of sphenoliths
are here interpreted to have evolved.
In well-preserved sphenoliths with triradiate elements,
their blades can be seen to form a honeycomb structure(see the scanning electron microscope [SEM] images in
Figures 2A, 5). The blades of each element are adjoined
to the blades of either adjacent elements, or the blades of
elements in the cycle above or below. Where the blades
from adjacent or higher/lower elements adjoin each other,
the suture where the blades meet is here termed a blade
junction (Figure 5). With diagenetic calcite overgrowth,
the space between the blades in each element is filled in,and the elements assume an overall lath shape. Not all elements in sphenoliths are triradiate. For example, the apical structure in S. heteromorphus is a monocrystalline,

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Figure 5: SEM photomicrographs of typical specimens of S. abies showing the triradiate-bladed shape of each element and the different types ofjunctions between adjacent blades. The distribution of two-, three- and four-element blade junctions imparts a pervasive asymmetry
to these specimens

biconical spine (Figure 3A, Plate 3, figs 7, 8). There areno published photographs of furcatoliths with triradiate elements, which may indicate that they are more susceptible
to diagenetic overgrowth than sphenoliths, or that bladed
elements are not a primary feature of furcatoliths.
In all sphenoliths, there are a greater number of elements in the proximal cycle than in the uppermost distal

cycle (i.e. the apical structure in most sphenoliths or thebifid spine in some sphenoliths). The lateral element cycles have intermediate numbers of elements. Where theelement count between two adjacent cycles differs by an
odd number, it is not possible for the blades in these cycles
to be adjoined in a regular way, where two blades (onefrom the lower cycle and one from the upper cycle) meetUltrastructure and taxonomy of the Sphenolithaceae

to form a blade junction. The difference in the element
count between adjacent cycles is accommodated by blade
junctions where three, or even four (rather than the usualtwo), blades meet. The apparently irregular distributionof two-, three- and four-element blade junctions throughout these sphenoliths results in a pervasive asymmetry
in the arrangement of elements in the sphenolith. Threeand four-element blade junctions have been observed inalmost all SEM photomicrographs of well-preserved S.
abies (Figure 5). It is assumed here that variable-element
blade junctions, and the pervasive asymmetry that resultsfrom these, are a characteristic of most, if not all, Sphenolithus species.
3.2 Calcite c-axis orientation andbirefringence patterns
In most sphenolithid species, the c-axis of the calcite crystal comprising each individual element is aligned with thelong axis of the element. For elements in the horizontal
plane (i.e. the plane of the microscope slide), the primarycontrol on birefringence is the angle between the long axisof the element and the polarising axes. When the medianaxis of the sphenolithid is aligned with one of the polarising axes, the elements with long axes that are near vertical or horizontal will be dark under cross-polarised light.
Elements with long axes that are near 45° to the polarisingaxes will be bright, and those with long axes between ~10
and 35° will be partially bright or dim.
In specimens where the blades of each element are
well-preserved, the orientation of each individual blade
affects the observed birefringence of the element. Bladesthat are at, or near, right angles to the plane of the microscope slide will have higher birefringence than the other two blades of the same element (when the element isbrightest; i.e. when its long axis is at 45° to the polarisingaxes), as they present a greater thickness of calcite relative
to the plane of the slide (i.e. the full width of the blade).
This is best observed in large specimens that are very wellpreserved (e.g. the holotype of S. acervus, Bown, 2005a,
pl. 43, fig. 15), and that may give the appearance of there
being more elements than are actually present. In most
specimens, where some overgrowth is present, this blade
effect is minimal compared to the overall orientation of
the element relative to the polarising axes and the planeof the slide.
In sphenolithids that possess a bifid spine (Figure 6),35

the c-axes of the elements in the bifid spine may not be
closely aligned with the long axis of each element, instead
being at an angle of ~10–45° to the median axis of the coccolith. For angles between ~30 and 45° between the c-axesof the bifid spine elements and the median axis, the spine
elements will be bright when the median axis is parallel toone of the polarising axes, and dark when the median axis
is at 45° to the polarising axes (see S. shamrockiae n. sp.,
Plate 2, figs 3, 4). For angles between 15 and 30°, the spine
elements will be dim (i.e. partially bright) at both parallel,
and at 45°, to the polarising axes (see Furcatolithus akropodus n. comb., Plate 4, figs 15, 16). For angles of lessthan 15°, the spine elements will be dark when parallel toone of the polarising axes, and bright at 45° to the polarising axes (see F. ciperoensis n. comb., Plate 4, figs 23, 24).
Many published light-microscope (LM) photomicrographs of sphenolithids are over-exposed, including theimages of many holotypes (e.g. the images of the holotype of S. belemnos in Bramlette & Wilcoxon, 1967 andS. capricornutus in Bukry & Percival, 1971). Because theelements of the four structural components in Sphenolithus (proximal cycle, lower lateral element cycle, upper
lateral cycle and apical structure) have c-axes that radiatefrom the core, each of the elements is dark when parallel
to one of the polarising axes, bright when at, or near, 45°,and neither fully bright nor dark when oriented obliquely
to the polarising axes. Recognition of the upper and lower
lateral cycles is generally easy in the LM, but can be very
difficult in over-exposed photographs, hindering the assignment of specimens in the LM to published species.
3.3 Proximal cycle
All sphenolithids share a proximal cycle (Young et al.,1997) of adpressed elements that are arranged radiallyin plan view (Figures 2, 3), often with slight imbricationand suture kinking (see pl. 2, fig. 4 in Wilcoxon, 1970).
In lateral view, the proximal cycle elements are approximately trapezoidal in outline. In well-preserved material,
the proximal cycle elements are bladed, with two sub-horizontal blades and one vertical blade extending laterally
from each element (see Figure 5C).
The elements of the proximal cycle vary in height andlateral extension of the base of the element relative to the
top (termed the degree of flare) between species. Some
species have minimal lateral extension of the base of theproximal cycle relative to the top (low degree of flare),

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Ultrastructure and taxonomy of the Sphenolithaceae

resulting in an approximately cylindrical proximal cyclewith a sub-vertical lateral periphery (e.g. S. dissimilis,
Plate 2, figs 23, 24). Others have strong lateral extensionof the base (high degree of flare), resulting in a proximal
cycle with a lateral periphery that is at a low angle to thevertical (e.g. S. delphix, Plate 3, figs 19–22). In lateralview, the basal surface of each element can be linear or
curved, resulting in the basal surface of the proximal cycle
being concave to a greater or lesser degree. The generalform of the proximal cycle is similar among all sphenolithid species, reflecting their common origin. The proximal
cycle has been termed the proximal shield or column by
Roth et al. (1971) and Perch-Nielsen (1985), the column
by Romein (1979) and Aubry (2014), and the basal feet byBown & Dunkley Jones (2012).
3.4 Lateral element cycles
All sphenoliths have two lateral element cycles (Young etal., 1997)––the lower and upper lateral element cycles––which lie above the proximal element cycle, and below
the apical structure, if one is present (Figures 1A–I, 2A, B,
3A, 4). In well-preserved material, it can be seen that theelements in the lateral cycles are bladed, with the bladesof each element joined at blade junctions to the blades inadjacent element cycles. In most species, the long axes ofthe lower lateral cycle elements are sub-horizontal in lat-

Figure 6 (left): Sketches showing the birefringence of taxa with a bifid
spine, indicating that the angle between the calcite c-axes in the bifid
spine elements and the median suture, and the orientation of the planeof the median suture of the bifid spine, relative to the plane of the slide,both strongly affect the birefringence observed in the bifid spine in the
LM. Only elements with the long axes lying parallel to the plane of theslide are shown. (A, B) Species with the c-axis of the bifid spine elements
lying between 0 and 15° to the median axis. (A) When the specimen isoriented with the plane of the median suture lying orthogonal to the slide,the bifid spine is dark (but not fully so) at 0° to the optical axes, andbright (but not fully so) at 45°. (B) When the same specimen is lying on
the slide with the plane of the median suture lying parallel to the slide, thebifid spine is fully dark at 0° to the optical axes, and fully bright at 45°.
(C, D) Species with the c-axis of the bifid spine elements lying between
15 and 30° to the median axis. (C) When the specimen is lying on theslide with the plane of the median suture lying orthogonal to the slide, thebifid spine is moderately bright at 0° to the optical axes, and also moderately bright at 45°. (D) When the same specimen is lying on the slide withthe plane of the median suture lying parallel to the slide, the bifid spine
is fully dark at 0° to the optical axes, and fully bright at 45°. (E, F) Species with the c-axis in the bifid spine elements lying between 30 and 45°
to the median axis. (E) When the specimen is lying on the slide with theplane of the median suture lying orthogonal to the slide, the bifid spine isfully bright at 0° to the optical axes, and dark at 45°. (F) When the same
specimen is lying on the slide with the plane of the median suture lying
parallel to the slide, the bifid spine is fully dark at 0° to the optical axes,
and fully bright at 45°

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eral view, and those of the upper lateral cycle elements lie
at approximately 45° to the median axis. Elements in eachof the lateral element cycles are arranged radially in planview. Other, similar cycles may exist above the two lateralcycles (see the discussion on the apical structure, below),
but in all sphenoliths, there are always two lateral element
cycles. The lateral element cycles vary between species intheir thickness, height and degree of lateral extension. The
lateral element cycles have been termed the basal cycles
by Romein (1979), the lower calyptra by Aubry (2014)
and the lateral elements by Roth et al. (1971) and PerchNielsen (1985).
Much confusion exists in the literature regarding theupper and lower lateral cycles and their distinction fromeach other, and from the proximal cycle, in cross-polarised
light. Many workers have referred to the four bright elements seen in the base of a typical sphenolith under crosspolarised light as the upper and lower basal quadrants or‘basal quads’ (Young et al., 1997; Bergen et al., 2017). The
lower quadrants are the birefringent elements of the proximal cycle, while the upper quadrants are the birefringent
elements of the two lateral element cycles. Many species
descriptions refer to the size ratios between the upper andlower quadrants.
This is problematic because, when a sphenolith is rotated relative to the polariser, the lower and upper lateralelement cycles alternate their birefringence relative to eachother. Effectively, the bright upper quadrants are reflecting
the birefringence of different elements as the sphenolith isrotated (the upper lateral element cycle is bright when the
median axis is parallel to one of the polarising axes, andthe lower lateral element cycle is bright when the medianaxis is at 45° to the polarising axes), making size ratios
between the upper and lower basal quadrants an unreliable
criterion for distinguishing between species, unless one isclear on which lateral cycle is bright when the size ratio is
being observed.
3.5 Apical structure
In most sphenolith species, there are one or more element
cycles above the upper lateral element cycle. The elementsin these cycles are arranged in lateral (i.e. horizontal) to
distal (i.e. vertical) orientations, radiating from the core
(Figures 1A–H, 2A, B, 3A, 4, 5). These form the apicalstructure. The apical structure can comprise either a single
element, termed a monocrystalline apical structure (Fig-

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ures 1E–G, 3A), or multiple elements, termed a composite
apical structure (Figures 1A–D, 2A, B). A composite apical structure may have a single cycle of elements, termeda monocyclic composite apical structure (Figures 1A–D,
2B, 4), or multiple cycles of elements, termed a polycyclic
composite apical structure (Figures 1A–C, 2A, 4). Where
there is a polycyclic composite apical structure (otherthan their position above the lateral element cycles), theelements in the apical cycles are usually minimally differentiated from the elements of the lateral element cycles(e.g. in species of the S. primus group). For all composite
apical structures, it can be seen in well-preserved material that the elements in the apical structure are bladed,with blades from each element joining at blade junctions
to the blades in adjacent element cycles (Figure 5). The
apical structure has been referred to as the apical spine byRoth et al. (1971), the cone or centro-distal spine by Romein (1979), the apical spine or apical elements by PerchNielsen (1985) and the upper calyptra by Aubry (2014).
The long-ranging S. primus group, from which all other sphenoliths are descended, has a polycyclic composite
apical structure that is hemispherical in shape. The evolution of new species of Sphenolithus involves modificationof this apical structure (and also changes in the shape of
the proximal cycle). There seems to be a trend in which a
lineage begins with a new species that evolves a monocyclic composite apical structure from a polycyclic ancestor in the S. primus group. Once a monocyclic composite
apical structure has been established, the apical structureoften becomes taller, turning into a monocrystalline apicalstructure in later species in the lineage. An example of thiscan be seen in the S. radians group, where S. editus, witha monocyclic composite apical structure, evolved from S.
moriformis (Plate 1, figs 5, 6) or S. apoxis (Plate 1, figs 9,10), with polycyclic composite apical structures. Later, S.
richteri, with a monocrystalline apical structure, evolved
from S. spiniger (Plate 1, figs 23, 24), with a monocyclic
composite apical structure. Monocrystalline apical structures have evolved from monocyclic composite apicalstructures several times, so species with monocrystalline
apical structures are clearly polyphyletic and cannot begrouped together.
Monocyclic composite apical structures with a conicalshape can be distinguished from monocrystalline apicalstructures with a similar shape by their diffuse extinction
when aligned with one of the major polarising axes (re-flecting multiple elements radiating from the core, at slightangles to each other, e.g. S. conicus, Plate 2, figs 29, 30),in contrast to the total extinction of a monocrystalline apical structure (e.g. S. heteromorphus, Plate 3, figs 7, 8). In
some species, there is a cycle of small, thin apical elements
above the upper lateral element cycle, above which there
is a tall monocrystalline apical structure (e.g. S. pseudoheteromorphus, Plate 3, figs 5, 6; also, see the holotype
specimen in Fornaciari & Agnini, 2009, pl. 1, fig. 1).
3.6 Bifid spine
In later members of the S. kempii group, the apical structure is reduced in height. The upper lateral element cycle
has grown vertically, and has a reduced element count,down to three or four elements in S. kempii (Figure 1G;
Plate 1, figs 27, 28), and two in S. shamrockiae n. sp. (Figure 1H; Plate 2, figs 3–6), S. furcatolithoides (Plate 2, figs
1, 2) and S. labradorensis (Figure 1I; Plate 2, figs 7–10).
With vertical growth of the upper lateral element cycle, theapical structure becomes relatively lower, eventually disappearing completely in S. furcatolithoides and S. labradorensis. Effectively, in S. furcatolithoides and S. labradorensis, with vertical growth of the upper lateral cycle, andreduction in the element count to two elements, the upper
lateral cycle becomes the dominant apical element, at theexpense of the apical structure, which has disappeared.
This highly modified upper lateral element cycle is heretermed the bifid spine and is a key characteristic of most
species in the genus Furcatolithus, which is descended
from the S. kempii group. The bifid spine becomes reducedin size in the F. triangularis group, becoming miniscule ordisappearing completely in the transition between F. avis
n. comb. (Plate 4, figs 27, 28) and F. umbrellus n. comb.
(Figure 1L; Plate 4, figs 29, 30)––the last representative of
the genus. The bifid spine has been referred to as a duocrystalline spine by Bown & Dunkley Jones (2012) andBergen et al. (2017).
There is considerably more variation in the birefringence pattern in the bifid spine in the furcatoliths (andthose sphenoliths in the S. kempii group that have a bifid
spine) than there is variation in the birefringence of theapical structure among most sphenoliths. Morphologically similar species can have essentially opposite birefringence patterns in the bifid spine under cross-polarised
light, based solely on differing c-axis orientations in thebifid spine (Figure 6). This is in contrast to most spheno-Ultrastructure and taxonomy of the Sphenolithaceae

liths (i.e. those that lack a bifid spine), where the c-axis
orientations are always parallel to the long axis of eachindividual element, so the birefringence of an element isbased largely on its position in the sphenolith structure andits thickness.
Because the bifid spine has two elements, separated
by a median plane, the orientation of the spine relative tothe plane of the microscope slide is critically important indetermining the observed birefringence of the spine undercross-polarised light. When the specimen is oriented sothat the median plane of the spine is horizontal (i.e. parallel to the slide), the bifid spine appears as a single elementin the LM (Figure 6b, d, f). When the median axis of thespecimen is aligned with one of the polarising axes, the bifid spine is dark, and when the specimen is aligned at 45°
to the polarising axes, it is bright. In this orientation (withthe median plane of the bifid spine being horizontal), theangle between the c-axes of the bifid spine elements andthe median axis of the coccolith (typically between 10°
and 45°) has no effect on the birefringence, so different
species, with different c-axis angles in the bifid spine, will
display similar birefringence.
In contrast, when the median plane of the bifid spine isvertical (i.e. at right angles to the plane of the slide), themedian plane appears as a sharp suture down the middleof the bifid spine (Figure 6a, c, e). The two elements ofthe spine are clearly visible, and their birefringence depends on the orientation of their c-axes in the horizontal
plane. The c-axes in the bifid spine elements are typicallybetween 10 and 45° to the median axis of the coccolith,so, depending on the c-axis orientation, the birefringencewhen the median axis is parallel to one of the polarisingaxes could be bright (for specimens with the c-axis between 35 and 45°: Figure 6e), dark (for specimens with thec-axis at an angle between 10 and 15°: Figure 6a) or dim(angles between 15 and 35°: Figure 6c).
The best example of this is S. labradorensis (Plate 2,
figs 7–10; junior synonym S. strigosus), which was illustrated with a median suture clearly visible, and bifid spine
elements that are brightly birefringent when parallel to thepolarising axes and dark at 45° (Firth, 1989, pl. 2, figs 15,16). The holotype of the otherwise similar S. runus (Bown& Dunkley Jones, 2006, pl. 8, figs 18–20), which is similarin size and has a similar range, has the median suture of
the bifid spine oriented obliquely to the plane of the slide.
The median suture is visible near the left and right edges

39of the spine, and the spine is mostly dark when parallelto the polarising axes and bright at 45°, opposite to thebirefringence observed in the bifid spine of S. labradorensis. The holotype of S. runus is here interpreted as beinga specimen of S. labradorensis where the median plane of
the bifid spine is slightly oblique to the horizontal, rather
than vertical. Accordingly, S. runus is considered here to
be a junior synonym of S. labradorensis.
In photomicrographs of well-preserved specimens ofsphenolithids with a bifid spine, many specimens show
long, thin extensions of the two bifid spine elements that
extend distally and laterally. These bifid spine extensions
sometimes extend to several times the height of the specimen below the spine extensions (see pl. 11, figs 7, 9, 18,
19, 22, 23, 25–29, 40, 41 in Bown & Newsam, 2017 for excellent illustrations of numerous species with bifid spinesthat bear long extensions). In most specimens, these bifid
spine extensions are missing, presumably because they
have broken off or dissolved.
4. Systematic palaeontology
With a relatively simple ultrastructure that was mostly conserved during the history of the family, separating sphenolithid species into an approximation of phylogenetic
lineages is difficult. Most of the variation among sphenolithid species is in the size and shape of components that areshared by most species. Previous studies that consideredsphenolithid ultrastructure and taxonomy include Roth etal. (1971), Romein (1979), Perch-Nielsen (1985), Younget al. (1997), Aubry (2014) and Bergen et al. (2017). Thesestudies classified sphenolithids into informal groups basedon varying combinations of overall shape, ultrastructuralunits and optical features. None of these studies recognised the full range of sphenolithid ultrastructure, particularly that lateral element cycles are present in all sphenoliths, that the lower lateral element cycle is not present inany furcatoliths, and that the bifid spine present in somesphenolith species and most furcatoliths is derived fromthe upper lateral element cycle of sphenoliths.
Also unrecognised in previous studies is the importance of the number of cycles in the apical structure ofsphenoliths (i.e. whether the composite apical structure ismonocyclic or polycyclic). Without considering whether
the apical structure is monocyclic or polycyclic, unrelated
species with superficially similar gross morphologies havebeen placed in the same group. Examples of this are clas-

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sification schemes that group the conical species Sphenolithus abies and S. radians together. These species are unrelated, but share a gross conical morphology. Sphenolithus
abies has a polycyclic composite apical structure with aconical shape, and was derived from the polycyclic S. primus lineage during the Neogene, while S. radians has amonocyclic composite apical structure with a similar conical shape, and was derived from a similar, but lower, spine
in S. editus, which in turn was derived from the polycyclic
S. primus lineage during the Eocene. The entire S. radians lineage was extinct well before S. abies evolved fromthe S. primus group, so classifying S. radians and S. abies
together because their disparate apical structures share aconical morphology obscures their differing phylogenies.
Similar arguments apply to classification schemes thathave grouped species with high proximal element cycles
that have curved elements, as seen in S. orphanknollensis,
F. umbrellus n. comb. and S. milanetti, a characteristic thatevolved separately in these unrelated species.
The approach taken here was to group Sphenolithus
species primarily by the nature of their apical structures,and secondarily by the shape of the proximal cycle (Figure7). Although necessarily speculative, this results in lineages that are plausibly phylogenetic. Species in the ancestraland long-lived S. primus lineage have a polycyclic composite apical structure, which varies in height and shape.
From this basal lineage, lineages with monocyclic apicalstructures diverged several times. In these lineages, an
initial monocyclic composite apical structure often gave
rise to monocrystalline apical structures before the lineage
went extinct (e.g. S. richteri, with a monocrystalline apicalstructure evolving from S. spiniger, which has a monocyclic composite apical structure). Species within lineages
tend to have proximal cycles that are similar in height anddegree of flare.
For species of Furcatolithus, which have much lessultrastructural variability than Sphenolithus species, theapproach taken here was to group the species based on
the angle between the median suture and the top of theproximal element cycle (Figure 1J, K), and also the heightof the proximal cycle as a proportion of the total height.
The size terms used here follow Young et al. (1997);
that is, <3 µm––small, 3–5 µm––medium, 5–8 µm––large,>8 µm––very large. These are used here to describe theheight of the coccolith, from the base of the proximal element cycle to the top of the apical structure, which formost sphenolithids is the largest dimension. For most furcatolith species, the height does not include the thin distal
and lateral extensions of the bifid spine, which can be as
long as 30 µm, but which are often missing due to breakage or dissolution. A representative subset of each of theinformal groups of sphenolithid species discussed here isillustrated on Plates 1–4.
Order DISCOASTERALES Hay, 1977 emend. Bown,
2010
Family SPHENOLITHACEAE Deflandre, 1952 emend.
Emended diagnosis: Domed, conical, cylindrical or biconical coccoliths with a proximal element cycle of radially and proximally oriented elements. Above the proximal element cycle, there is usually one or more cycles ofradially to distally arranged elements. The calcite c-axes
in each element are usually oriented parallel to the longaxis of the element. All of the elements radiate from apoint on the median axis, just above the proximal cycle.
Included genera: Sphenolithus, Furcatolithus. Range:
Paleocene (Late Danian) to Pliocene (Zanclean). Discussion: The original description for the family by Deflandre(1952) is “Sphenoliths, or wedge-shaped bodies, with adistinctive ‘spherolithic’ structure, producing a black crossin cross polarised light, when positioned longitudinally”(translation from Aubry, 2014). This was understood here
to mean that when sphenolithid specimens are viewed laterally, with the long axis of the specimen aligned with oneof the polarising axes, that a black cross is visible on thespecimen, with the axes of the cross being aligned withthe polarising axes. While such a birefringence pattern isshown by many sphenolithid species, it is not shown by
any furcatolith species, or by any sphenolith species thathave a bifid spine (e.g. S. furcatolithoides). Accordingly,
the family is emended here.
Genus Sphenolithus Deflandre, 1952 emend.
Emended diagnosis: Domed, conical, cylindrical or bi-

Figure 7 (right): Range chart showing the stratigraphical distributionsof the species groupings used in this study. Ranges based on Bergen etal. (2017), Bown & Dunkley-Jones (2012) and Aubry (2014). All measurements are based on the author’s measurements of the holotype orparatype images. All sketches were traced from the holotype or paratype
imagesUltrastructure and taxonomy of the Sphenolithaceae

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conical coccoliths with a proximal element cycle situatedbelow two radially oriented, vertically superimposed element cycles––the lower and upper lateral element cycles.
Above the upper lateral element cycle, an apical structure isusually present. The apical structure may comprise single
or multiple cycles of vertically stacked, radially and distally oriented elements, or a single vertical to sub-vertical element, or may be entirely absent. Type species: Sphenolithus radians Deflandre, 1952. Synonyms: Nannoturbella
Brönnimann & Stradner, 1960, the generotype of which is
Nannoturbella moriformis Brönnimann & Stradner, 1960,a species that clearly belongs in Sphenolithus. Sphenaster Wilcoxon, 1970, the generotype of which, Sphenaster
metula Wilcoxon, 1970, is an isolated proximal element
cycle of a sphenolith, probably from the S. primus group.
Discussion: In the sphenolith lineage (the S. kempii group)that give rise to the genus Furcatolithus, the upper lateralelement cycle increases in size vertically, with the number of elements reducing to two and becoming the bifid
spine present in most species of Furcatolithus. The apicalstructure is completely absent in the last members of thislineage––S. furcatolithoides and S. labradorensis.
The origin of S. primus (and hence the genus Sphenolithus and the family Sphenolithaceae) is likely related to
the genus Diantholitha (as noted by Aubry, 2014), which
has a very similar proximal cycle to S. primus. Above theproximal cycle, Diantholitha species have a single radialcycle of upward- and outward-extending apical elements.
As in S. primus, the calcite c-axes of the elements lie parallel to their long axes. The addition of extra cycles of elements distally to form both the lateral and apical element
cycles of Sphenolithus seems a plausible mechanism forthe evolution of Sphenolithus from Diantholitha. The generotype of Diantholitha, D. mariposa Rodriguez & Aubryin Aubry et al., 2011 is illustrated on Plate 1, figs 1, 2 forcomparison.
The holotype of S. elongatus Perch-Nielsen, 1980 (pl.
2, figs 5, 6) does not appear to have an ultrastructure thatbelongs to either Sphenolithus or Furcatolithus. What
superficially appears to be a proximal element cycle has
elements that do not resemble those of any other sphenolithid. No lateral cycle elements appear to be present, andno median suture appears in the spine. Accordingly, thisspecies was not considered to be a true sphenolithid and is
not considered further.
The genus Ilselithina Stradner in Stradner & Adamiker,

1966 has small to medium biconical coccoliths that havebeen considered by Aubry (2014) and Bergen et al. (2017)
to be possibly related to Sphenolithus, based largely on thesimilarity between their proximal element cycles. Youngin Young et al. (2018) noted that the elements consideredby previous studies to belong to separate proximal and distal cycles, are actually one piece, with the elements thatappear to belong to the distal cycle actually being distal
extensions of the proximal cycle elements. This construction is quite unlike any sphenolithid, so Ilselithina was notconsidered to be a member of the Sphenolithaceae, and is
not considered here.
Forty-eight species in the genus Sphenolithus wererecognised as valid in this study. These species have been
divided into eight informal groups of species, based onshared morphology and likely phylogeny. These groups
are listed in Table 1 and detailed below, with both groups
and species approximately ordered by first stratigraphic
appearance. A selection of species from each group is illustrated on Plates 1–3.
Sphenolithus primus GroupThe species in this group all have simple domed morphologies and a polycyclic composite apical structure with multiple apical element cycles, which are minimally differentiated from the lower and upper lateral element cycles.
This group is long-ranging, with representatives present
throughout the history of the genus, forming a plexus ofclosely related species of varying sizes, and with varying
apical structure heights. All other groups of sphenolithids
evolved from this group.
The species in this group are discussed below in approximate order of first stratigraphic appearance: S. primus, S. acervus, S. moriformis, S. apoxis, S. puniceus, S.
neoabies, S. abies, S. verensis and S. grandis. Range charts
for this group are presented in Figures 8–10.
Sphenolithus primus Perch-Nielsen, 1971aPl. 1, figs 3, 4
1971a Sphenolithus primus Perch-Nielsen: p. 357, pl. 11,
Figure 8 (right): Range chart for the S. primus, S. conicus and S. quadrispinatus groups. Ranges based on Bergen et al. (2017), Bown & Dunkley-Jones (2012) and Aubry (2014). All measurements are based on theauthor’s measurements of the holotype or paratype images. All of thesketches were traced from the holotype (HT) or paratype (PT) images,
either LM or EM

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Table 1: Species of Sphenolithus grouped into informal morphological groups, in approximate order of first stratigraphic appearance (see Figure 7)
GROUP

MORPHOLOGICAL CRITERIONRANGE

S. primus

Simple domed shape
Polycyclic composite apical structure

S. anarrhopus

Conical shape
High, sharply pointed monocrystalline apical structure

S. radians

Conical shape
Monocyclic composite or monocrystalline apical structure

S. kempii

Divergent upper lateral element cycle
Trend of increasing upper lateral element length, with reduction in element countS. dissimilis

Polycyclic composite apical structure with subparallel to divergent elements

S. conicus

Conical shape
Medium to high, sharply pointed to rounded monocyclic or monocrystalline apical structure

S. delphix

Strongly flared proximal element cycle
Monocyclic or monocrystalline apical structure

S. quadrispinatus Monocyclic apical structure with divergent elements with thin lateral and distal extensions

fig. 4; pl. 12, figs 4, 5, 7–12, pl. 14, figs 22–24.
1997 Sphenolithus primus Perch-Nielsen, 1971a – Bybell& Self-Trail: pl. 5, fig. 8.
2008 Sphenolithus primus Perch-Nielsen, 1971a – Steurbaut & Sztrákos: pl. II, figs 5, 6.
2014 Sphenolithus primus Perch-Nielsen, 1971a – Khalil& Al Sawy: pl. 8, figs 17, 18.
Diagnosis: A small sphenolith with a medium-height,
slightly conical proximal element cycle, thin lower andupper lateral element cycles, and polycyclic composite
apical element cycles forming a low apical dome. Remarks: This was the first sphenolithid species to evolve.
Given that Diantholitha evolved in NP4 in the Danian, and

SPECIES

Early Paleocene–Early Pliocene S. primus(Danian–Zanclean)S. acervus
S. moriformis
S. bergenii
S. apoxis
S. puniceus
S. neoabies
S. abies
S. verensis
S. grandis
Late Paleocene–Early Eocene S. anarrhopus(Thanetian–Ypresian)S. villae
S. conspicuus
Early Eocene–Early Oligocene S. editus(Ypresian–Rupelian)
S. arthurii
S. radians
S. orphanknollensis
S. spiniger
S. richteri
S. pseudoradians
Middle Eocene
S. stellatus(Lutetian–Bartonian)S. kempii
S. perpendicularis
S. shamrockiae
S. furcatolithoides
S. labradorensis
Late Eocene–Early Miocene
S. truaxii(Priabonian–Burdigalian)S. procerus
S. capricornutus
S. compactus
S. disbelemnos
S. multispinatus
S. dissimilis
S. cometa
Early Oligocene–Middle Miocene S. conicus(Rupelian–Serravallian)S. calyculus
S. macroacanthos
S. pseudoheteromorphus
S. heteromorphus
S. preasii
S. milanetti
Early Oligocene–Early Miocene S. bipedis(Rupelian–Burdigalian)S. spinula
S. microdelphix
S. delphix
S. tintinnabulum
S. belemnos
Late Miocene
S. quadrispinatus(Tortonian)

was likely the ancestor of S. primus, it is clear that the first
S. primus evolved in NP4. However, Diantholitha was notdescribed (Aubry in Aubry et al., 2011) until well after
S. primus had been described (Perch-Nielsen, 1971a) and,given the strong similarity between the side views of Diantholitha and S. primus, it is possible that some records inthe literature of the earliest S. primus are actually records
of Diantholitha. The simple morphology of S. primus islong-lived, persisting to the end of the Zanclean in S. moriformis, a larger, but otherwise similar, species.
Sphenolithus acervus Bown, 2005a
2005a Sphenolithus acervus Bown: pl. 43, figs 13–19.

Ultrastructure and taxonomy of the Sphenolithaceae

Diagnosis: A large sphenolith with a medium-height,
slightly conical proximal element cycle, thick lower andupper lateral element cycles, and polycyclic composite
apical element cycles forming a medium-height apicaldome. Remarks: Individual elements in this species appear very strongly triradiate, resulting in a relatively open
structure in three dimensions. This explains why this large
species only has moderate birefringence, rather than thehigh birefringence exhibited by similarly large species
in this group, such as S. puniceus, which has coarser elements and high birefringence, with first-order red and blue
colours under cross-polarised light.
Sphenolithus moriformis (Brönnimann & Stradner,
1960) Bramlette & Wilcoxon, 1967
Pl. 1, figs 5, 6
1960 Nannoturbella moriformis Brönnimann & Stradner:
p. 368, figs 11–13, 16, non figs 14, 15.
1965 Sphenolithus pacificus Martini: p. 407, pl. 36, figs
7–10.
1967 Sphenolithus moriformis (Brönnimann & Stradner,
1960) Bramlette & Wilcoxon: p. 124, pl. 3, figs 1–4,
non figs 5, 6.
2012 Sphenolithus moriformis (Brönnimann & Stradner,
1960) Bramlette & Wilcoxon, 1967 – Bown & Dunkley Jones: pl. 13, fig. 37.
Diagnosis: A medium-sized sphenolith with a low to
medium-height proximal element cycle, thin lower andupper lateral element cycles, and polycyclic composite
apical cycles forming a low apical dome. Remarks: Brönnimann & Stradner (1960) illustrated Nannoturbella moriformis with a series of line-drawings featuring two different morphotypes––a low-domed form (their figs 11–13,
16), which they clearly designated as the holotype, anda higher-domed form (their figs 14, 15), which was later
described as S. apoxis by Bergen & de Kaenel in Bergen etal. (2017). The transition from S. primus to S. moriformis
is unclear, as there is little difference between the two species, other than size (the holotype of S. primus is ~3.5 µm
high, that of S. moriformis is ~5 µm high). Most authors,
somewhat arbitrarily, have placed this transition aroundthe base of the Eocene. Sphenolithus moriformis has thelongest range of all sphenolithid species, from the basal
Eocene to the mid-Pliocene.

45

Sphenolithus bergenii n. sp.
Pl. 1, figs 7, 8
non 1980 Sphenolithus compactus Backman: p. 59, pl. 3,
fig. 20.
Derivation of name: Named in honour of Dr Jim Bergen, retired Amoco and BP nannofossil biostratigrapher
and mentor. Diagnosis: A very small to small sphenolithwith a low, moderately flared proximal element cycle, thinlower and upper lateral element cycles, and a low-domed
apical structure. Remarks: Small sphenoliths with a lowdomed apical structure have been placed in S. compactus
by most workers, largely following Perch-Nielsen (1985,
pp. 522, 523, fig. 71, based on sketches in Aubry, 1989).
Perch-Nielsen (1985, fig. 71) provided three sketches of S.
compactus––two showing its appearance in the LM, andone an interpretation of what the species would look likein the EM. The two sketches showing the appearance ofS. compactus in the LM show a form with a low proximal
cycle, while the figure illustrating its appearance in the
EM shows a tall, cylindrical proximal cycle, much like theholotype of S. compactus and unlike the other two sketches. Holotype: Pl. 1, figs 7, 8. Holotype height: 2.7 µm.
Type locality: DSDP Leg 12, Hole 116, Rockall Plateau,
Atlantic Ocean. Type level: DSDP-12-116, 12-1, 80–81
cm; NN3 (of Martini, 1971), Burdigalian. Occurrence:
The range of this species has not been fully established
due to the taxonomic confusion with S. compactus. In the
distribution data for a composite section through most of
the Oligocene and Neogene in ODP Leg 154 holes, Bergen
et al. (2019b) recorded this species as S. compactus (which
they distinguished from S. paratintinnabulum, which, as
discussed in this paper, is a junior synonym of S. compactus) throughout, from the base of their dataset at ~30.7 Ma,
up to 3.607 Ma, just below the extinction of the genus.
Sphenolithus apoxis Bergen & de Kaenel in Bergen etal., 2017
Pl. 1, figs 9, 10
1960 Nannoturbella moriformis Brönnimann & Stradner:
p. 368, figs 14, 15, non figs 11–13, 16.
1967 Sphenolithus moriformis (Brönnimann & Stradner,
1960) Bramlette & Wilcoxon: p. 124, pl. 3, figs 5, 6,
non figs 1–4.

Howe

Figure 9: Range chart for the S. primus, S. anarrhopus, S. radians and S. kempii groups. Ranges based on Bergen et al. (2017), Bown & DunkleyJones (2012) and Aubry (2014). All measurements are based on the author’s measurements of the holotype or paratype images. All sketches weretraced from the holotype or paratype images, either LM or EM

46

Ultrastructure and taxonomy of the Sphenolithaceae

472017 Sphenolithus apoxis Bergen & de Kaenel in Bergen
et al.: pl. 2, figs 11–20.

Sphenolithus abies Deflandre in Deflandre & Fert, 1954
Pl. 1, figs 15, 16

Diagnosis: A medium-sized sphenolith with a mediumheight, slightly flared proximal element cycle, thin lower
and upper lateral element cycles, and a polycyclic composite apical structure forming a high apical dome. Remarks: This species is essentially a high-domed, rather
than low-domed, form of S. moriformis. It forms a plexus
with S. moriformis for its entire range, from the Ypresianto the Burdigalian.

1953 Sphenolithus abies Deflandre: p. 1786.
1954 Sphenolithus abies Deflandre in Deflandre & Fert: p.
50, pl. X, figs 1–4.
2017 Sphenolithus abies Deflandre in Deflandre & Fert,
1954 – Bergen et al.: pl. 2, figs 5–10.

Sphenolithus puniceus Bergen & de Kaenel in Bergen etal., 2017
Pl. 1, figs 11, 122017 Sphenolithus puniceus Bergen & de Kaenel in Bergen et al.: pl. 1, figs 19–26.
Diagnosis: A large sphenolith with a medium-height proximal element cycle, thick lower and upper lateral element
cycles, and polycyclic composite apical element cycles
forming a medium-height apical dome. All of the elements
appear coarsely constructed, although this is probably afunction of the large size of the sphenolith. Remarks:
The large size and coarse elements of this species resultin high birefringence relative to most other sphenolithids,
with first-order orange, red and blue colours under crosspolarised light.
Sphenolithus neoabies Bukry & Bramlette, 1969
Pl. 1, figs 13, 14
1969 Sphenolithus neoabies Bukry & Bramlette: pl. 3, figs
9–11.
2017 Sphenolithus neoabies Bukry & Bramlette, 1969 –Bergen et al.: pl. 1, figs 1–4.
Diagnosis: A small sphenolith with a low, strongly flared
proximal element cycle, thin lower and upper lateral element cycles, and polycyclic composite apical element cycles forming a very low, pointed apical dome. Remarks:
The strongly flared proximal cycle and small pointed apical structure of this species give it a distinctive triangularlateral outline.

Diagnosis: A medium to large sphenolith with a mediumheight, moderately flared proximal element cycle. The
lower and upper lateral element cycles are thin. The apicalstructure is composite and polycyclic, and has the form ofa high, rounded cone. Remarks: Along with S. moriformis, this species is consistently common throughout thelate Middle Miocene to Early Pliocene interval.
Sphenolithus verensis Backman, 1978
Pl. 1, figs 17, 18
1978 Sphenolithus verensis Backman: p. 111, pl. 2, figs
4–6, 11, 12.
2017 Sphenolithus verensis Backman, 1978 – Bergen etal.: pl. 2, figs 1–4.
Diagnosis: A large sphenolith with a medium-height,
strongly flared proximal element cycle. The lower andupper lateral element cycles are thin. The apical structure
is composite and polycyclic, and has the form of a high,rounded cone. Remarks: The strongly flared proximal element cycle is the only significant difference between thisspecies and S. abies.
Sphenolithus grandis Haq & Berggren, 1978
1978 Sphenolithus grandis Haq & Berggren: figs 17, 18.
2017 Sphenolithus grandis Haq & Berggren, 1978 – Bergen et al.: pl. 1, figs 27–30.
Diagnosis: A large sphenolith with a medium-height proximal element cycle, thick lower and upper lateral element
cycles, and polycyclic composite apical element cycles
forming a medium-height apical dome. Remarks: Thislarge species is essentially a large form of S. moriformis.
The birefringence of this species reaches first-order yellow
and orange––higher than S. moriformis, as its elements areHowe

Figure 10: Range chart for the S. primus, S. dissimilis and S. delphix groups. Ranges based on Bergen et al. (2017), Bown & Dunkley-Jones (2012)
and Aubry (2014). All measurements are based on the author’s measurements of the holotype or paratype images. All sketches were traced from theholotype or paratype images, either LM or EM

48

Ultrastructure and taxonomy of the Sphenolithaceae

larger and thicker, but lower than the first-order red andblue birefringence exhibited by S. puniceus.
Sphenolithus anarrhopus GroupThe species in this group are all conical, with a high,sharply pointed, monocrystalline or monocyclic composite
apical structure. In most specimens, the apical structure ismonocrystalline, but occasionally (e.g. S. villae in Bown,
2005a, pl. P9, figs 23, 24, 35, 36) it can be seen that theapical structure is composite and monocyclic, comprising
several elements, but with one larger element dominating
the spine. This is the first group of sphenolithids to diverge
from the simple-domed morphologies of the S. primusgroup. The species in this group are discussed below inapproximate order of first stratigraphic appearance: S. anarrhopus, S. villae and S. conspicuus. A range chart forthis group is presented in Figure 9.
Sphenolithus anarrhopus Bukry & Bramlette, 1969
Pl. 1, figs 19, 20
1969 Sphenolithus anarrhopus Bukry & Bramlette: pl. 3,
figs 5–8.
2005a Sphenolithus anarrhopus Bukry & Bramlette, 1969
– Bown: pl. 44, figs 2–5.
2008 Sphenolithus rioi Agnini et al.: pl. 2, figs 3–8.
Diagnosis: A large, conical sphenolith with a mediumheight proximal element cycle, a thin lower lateral element cycle, a thick upper lateral element cycle, and a tall,
sharply pointed, conical monocrystalline apical structure.
The apical structure is usually slightly asymmetric withrespect to the median axis of the sphenolith. Remarks:
Sphenolithus rioi was described as having a straight spinethat is generally longer than the spine of S. anarrhopus.
The holotypes of the two species are very similar in size
(6.8 µm for S. rioi and 7.0 µm for S. anarrhopus), withsimilarly sized spines. Whilst most specimens of S. anarrhopus have slightly asymmetric apical structures, it
seems clear that even with an asymmetric spine, if thespine is pointing downwards or upwards relative to theplane of the slide, it would appear to be symmetrical inplan view. For these reasons, S. rioi is considered to be ajunior synonym of S. anarrhopus.

49

Sphenolithus villae Bown, 2005a
2005a Sphenolithus villae Bown: pl. 44, figs 11–24.
2005b Sphenolithus villae Bown, 2005a – Bown: pl. P9,
figs 28–30.
Diagnosis: A very large, conical sphenolith with a high,slightly flaring proximal element cycle, a thin lower lateralelement cycle, a thick upper lateral element cycle, and avery tall, pointed, conical monocyclic composite or monocrystalline apical structure. Remarks: Distinguished fromthe otherwise similar S. anarrhopus and S. conspicuus byits symmetrical apical structure and larger size.
Sphenolithus conspicuus Martini, 1976
1976 Sphenolithus conspicuus Martini: pl. 13, figs 1–3.
2012 Sphenolithus conspicuus Martini, 1976 – Bown &Dunkley Jones: pl. 10, figs 16–18.
Diagnosis: A large conical sphenolith with a mediumheight cylindrical proximal element cycle, a thin lower
lateral element cycle, a slightly thickened upper lateral element cycle, and a tall conical apical structure. Remarks:
Sphenolithus conspicuus has a symmetrical apical structure and is taller and narrower than S. anarrhopus, but isotherwise similar.
Sphenolithus radians GroupSpecies in this group all have a conical shape and a monocyclic composite or monocrystalline apical structure. They
are clearly differentiated from species of the S. primusgroup, which all have polycyclic apical structures. The
species in this group are discussed below in approximate
order of first stratigraphic appearance: S. editus, S. arthurii, S. radians, S. orphanknollensis, S. spiniger, S. richteri
and S. pseudoradians. A range chart for this group is presented in Figure 9.
Sphenolithus editus Perch-Nielsen in Perch-Nielsen etal., 1978
1978 Sphenolithus editus Perch-Nielsen in Perch-Nielsen
et al.: p. 352, pl. 8, figs 22–27; pl. 20, figs 5–19.
1997 Sphenolithus editus Perch-Nielsen in Perch-Nielsen
et al. (1978) – Bybell & Self-Trail: pl. 5, figs 9, 12.

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2012 Sphenolithus editus Perch-Nielsen in Perch-Nielsen
et al. (1978) – Bown & Dunkley Jones: pl. 10, figs 3, 4.
Diagnosis: A small, conical sphenolith with a mediumheight, moderately flared proximal element cycle, thinlower and upper lateral element cycles, and a mediumheight, pointed, conical monocyclic composite apicalstructure. Remarks: SEM photomicrographs of this small
species by Bybell & Self-Trail (1997, pl. 5, figs 9, 12)
clearly show that the apical structure is composite andmonocyclic, with vertically oriented, blade-shaped elements. The apical structure is very similar in appearance tothat of S. radians (see the SEM photomicrograph of PerchNielsen, 1977, pl. 31, fig. 8).
Sphenolithus arthurii Bown, 2005b
2005b Sphenolithus arthurii Bown: p. 9, pl. 9, figs 1–7.
Diagnosis: A large to very large, stoutly constructed,
conical sphenolith, with a medium-height, slightly flaring
proximal element cycle, thick lower and upper lateral element cycles, and a medium-height, pointed, conical monocyclic composite apical structure. Remarks: This species
appears to be restricted to the Early Eocene. It is essentially a heavily constructed form of S. radians, but with alower apical structure.

1971b Sphenolithus orphanknolli Perch-Nielsen: p. 56, pl.
3, figs 1–3; non pl. 7, figs 30–32.
1972 Sphenolithus orphanknolli Perch-Nielsen, 1971b –Perch-Nielsen: pl. 17, fig. 2.
1978 Sphenolithus orphanknolli Perch-Nielsen, 1971b –Proto Decima et al.: pl. 12, figs 4a–c, 5a–d.
non 2012 Sphenolithus orphanknollensis Perch-Nielsen,
1971b – Bown & Dunkley Jones: pl. 10, figs 19–24.
Diagnosis: A medium-sized, conical sphenolith, with ahigh, moderately flaring proximal element cycle. In lateral view, the elements in the proximal element cycle areslightly curved, with the concave side facing down. The
lower and upper lateral element cycles are thin, and there
is a low, slightly rounded, conical monocyclic composite
apical structure. Remarks: The holotype of this species
is a high-quality SEM image (Perch-Nielsen, 1971b, pl.
3, fig. 2) that clearly shows a high proximal cycle withcurved elements, thin lateral element cycles, and a low
monocyclic composite apical structure (the apical structure is much lower, but otherwise strongly resembles thatof S. radians Deflandre, 1952). The LM images (pl. 7, figs
30–32) in Perch-Nielsen (1971b) and Bown & Dunkley
Jones (2012, pl. 10, figs 19–24) show other specimens that
do not have a high, arcuate proximal cycle, and these are
not considered here to belong to S. orphanknollensis.

Sphenolithus radians Deflandre, 1952

Sphenolithus spiniger Bukry, 1971aPl. 1, figs 23, 24

1952 Sphenolithus radians Deflandre: p. 466, figs 363A–
G.
2015 Sphenolithus radians Deflandre, 1952 – Fioroni etal.: pl. 2, figs 11, 12.

1971a Sphenolithus spiniger Bukry: p. 322, pl. 6, figs
10–12.
2012 Sphenolithus spiniger Bukry, 1971a – Bown &Dunkley Jones: pl. 10, figs 5, 6.

Diagnosis: A medium to large, conical sphenolith, witha medium-height, slightly flared proximal element cycle,
slightly thick lateral element cycles, and a high, conical,
sharply pointed, monocyclic composite apical structurewith vertically oriented, blade-shaped elements. Remarks: This long-ranging species is the generotype ofSphenolithus, and was the first Sphenolithus species described.

Diagnosis: A small to medium, conical sphenolith, with ahigh and moderately flaring proximal element cycle, a thinlower lateral element cycle, a thick upper lateral element
cycle, and a conical, pointed monocyclic composite apical structure. Remarks: This small species is easily distinguished from S. editus by its higher proximal cycle andlower apical structure.
Sphenolithus richteri Bown & Dunkley Jones, 2012

Sphenolithus orphanknollensis Perch-Nielsen, 1971bPl. 1, figs 21, 22

2012 Sphenolithus richteri Bown & Dunkley Jones: p. 33,

Ultrastructure and taxonomy of the Sphenolithaceae

pl. 11, figs 7–12.
Diagnosis: A small, conical sphenolith, with a mediumheight, cylindrical proximal element cycle, thin lower
lateral cycle elements, thick upper lateral cycle elements,
and a narrow, sharply pointed, monocrystalline apicalstructure. Remarks: This species has a monocrystalline
apical structure, and is clearly descended from S. spiniger, which has a monocyclic composite apical structure.
No other Sphenolithus species with a monocrystalline apical structure exist when S. richteri first occurs in the midEocene. This indicates that S. richteri is not descended
from the earlier S. anarrhopus lineage of sphenoliths withmonocrystalline apical structures, thus demonstrating thatmonocrystalline apical structures are polyphyletic.
Sphenolithus pseudoradians Bramlette & Wilcoxon,
1967
Pl. 1, figs 25, 26
1967 Sphenolithus pseudoradians Bramlette & Wilcoxon:p. 126, pl. 2, figs 12–14.
2005b Sphenolithus pseudoradians Bramlette & Wilcoxon, 1967 – Bown: pl. P9, figs 19, 20.
Diagnosis: A very large, conical sphenolith, with a low
to medium-height, slightly flared proximal element cycle,
thick lateral element cycles, and a high, conical, sharply
pointed monocyclic composite apical structure. Remarks:
This species is essentially a larger and more robustly constructed variety of S. radians.
Sphenolithus kempii GroupThe species in this group all have low to medium-heightproximal element cycles and a thin lower lateral element
cycle. The apical structure is monocyclic and reduced insize, disappearing completely in S. furcatolithoides andyounger species. With a reduction in element count in theupper lateral element cycle through time, ultimately to twoelements in S. perpendicularis, the upper lateral cycle elements increase in length laterally and vertically throughtime, to become the bifid spine of S. shamrockiae n. sp.
and younger species.
The species in this group are discussed below in approximate order from first stratigraphic appearance: S.
stellatus, S. kempii, S. perpendicularis, S. shamrockiae n.

51sp., S. furcatolithoides and S. labradorensis. A range chart
for this group is presented in Figure 9.
Sphenolithus stellatus Gartner, 1971
1971 Sphenolithus stellatus Gartner: p. 114, pl. 5, fig. 3a,b.
1995 Sphenolithus stellatus Gartner, 1971 – Bralower &Mutterlose: pl. 7, figs 27, 28.
2006 Sphenolithus stellatus Gartner, 1971 – Lupi & Wise:
pl. 2, figs 23, 24.
Diagnosis: The type illustrations in Gartner (1971, pl.
5, fig. 3a, b) are black and white photomicrographs of asingle specimen in a single orientation (plan view), so theexact ultrastructure of this species is unclear. It appears
to have an upper lateral element cycle comprising at least
four, and probably six, elements. Other elements are present between these four elements, but these are slightly out
of focus, suggesting they may be lower lateral cycle elements. Without images of lateral views of this species,
it is difficult to fully characterise the proximal and lower
lateral element cycles, or the apical structure. The typespecimen is ~9.4 µm wide. Remarks: This species is interpreted here as an intermediate form between S. spiniger
and S. kempii, or perhaps between S. kempii and S. perpendicularis. With at least four large, distally and laterally
divergent spines in the upper lateral element cycle, thisspecies is far less likely than most other sphenolith species to lie on its side on the microscope slide, being more
likely to lie top-up or top-down, so it has only been figured
in plan view and not lateral view. If there are only four
divergent spines, it is possible that this species is a seniorsynonym of S. kempii. Until this species has been figured
in side view, and its exact relationship to S. kempii and/or S. perpendicularis has been made clear, it was decided
here to retain it as a separate species.
In his original description, Gartner (1971, p. 114) described the type level of S. stellatus (and separately in the
figure caption for the holotype) as being a sample at 251
ft in JOIDES Core J-6B, offshore Florida. The summary range chart for the JOIDES cores studied by Gartner(1971, fig. 2) showed the sample from 251 ft in Core J-6B
as belonging to his Isthmolithus recurvus Zone of Late Eocene age, but the nannofossil distribution chart for Core
J-6B (Gartner, 1971, fig. 5) does not show any occurrence

52

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of S. stellatus. Gartner (1971, p. 114) described the occurrence of S. stellatus as “the middle Eocene interval of the
JOIDES Blake Plateau Core J-3”, with no further information given. The nannofossil distribution chart for Core J-3(Gartner, 1971, fig. 4) showed S. stellatus occurring as rare
to few in samples from 516–536 ft, an interval belonging
to his Chiphragmalithus quadratus and Reticulofenestra
umbilica Zones, which he regarded as being of latest Earlyand Middle Eocene age. These two zones are shown as
being equivalent to planktonic foraminiferal zones P10
and P11 (using the planktonic foraminiferal zonation ofBlow, 1979), which are Middle Eocene in age (Wade etal., 2011).
The best guide we have to the actual age of this taxon, which has rarely been recorded since being described(suggesting it has a very short range), is the distribution
data of Bralower & Mutterlose (1995), who record S. stellatus from ODP Holes 865B and 865C in the mid-Pacific.
They recorded its occurrence from Section 8H-6 in Hole
865B and 9H-3 in Hole 865C, at the base of CP13a (ofOkada & Bukry, 1980)/within NP15 (of Martini, 1971), toSection 7H-6 in Hole 865B and 8H-3 in Hole 865C, low
in CP13b/within NP15. This species has also been recorded by Lupi & Wise (2006) from ODP Hole 1260A on theDemerara Rise. They recorded occurrences of S. stellatus
from Section 21R-2, in the uppermost part of CP12a/NP14
to Section 18R-6 at the base of CP13b/within NP15. Fromthese records, it seems that the range is essentially within
CP13a/NP15, which closely matches the range from JOIDES Blake Plateau Core J-3 (Gartner, 1971, fig. 4), andalso the range of S. kempii (Bown & Dunkley Jones, 2012,
p. 33). It seems clear that S. stellatus is closely related to
S. kempii, and has a similarly short range.
Sphenolithus kempii Bown & Dunkley Jones, 2012
Pl. 1, figs 27, 28
1990 Sphenolithus sp. 1 Okada: p. 154, pl. 2, figs 9–12.
2012 Sphenolithus kempii Bown & Dunkley Jones: p. 33,
pl. 10, figs 25–30, 32–35.
2012 Sphenolithus cf. S. kempii Bown & Dunkley Jones:p. 33, pl. 10, figs 36, 37.
2015 Sphenolithus kempii Bown & Dunkley Jones, 2012 –Fioroni et al.: pl. 1, figs 19–24.
Diagnosis: Medium-sized sphenolith with a medium-height, cylindrical proximal element cycle and a thin lower lateral element cycle. The upper lateral element cycle
has a reduced element count, with three or four elementsthat are elongated vertically and laterally, forming distally
divergent spines. The calcite c-axes in the upper lateralcycle elements are at an angle of ~45° to the median axis,
so when the long axis of an element is parallel to the planeof the slide, and the median axis of the sphenolith is parallel to one of the polarising axes, the element is bright, andwhen the median axis is at 45°, it is dark. A small apicalstructure may be present, which appears to be monocyclic
and monocrystalline. Remarks: This species, which appears to be descended from S. spiniger, marks the beginning of a lineage in which the upper lateral element cycle
grows vertically and laterally, ultimately becoming the bifid spine that characterises most Furcatolithus species. It
is possible that S. stellatus (Gartner, 1971, p. 114, pl. 5, fig.
3a, b) is a plan view of S. kempii, in which case, S. kempii
would be a junior synonym of S. stellatus. Until this can beshown conclusively, the name S. kempii is retained here.
Sphenolithus perpendicularis Shamrock, 2010
Pl. 1, figs 29, 30
1995 Sphenolithus “spinatus” Bralower & Mutterlose: p.
59, pl. 7, figs 29, 30.
2010 Sphenolithus perpendicularis Shamrock: p. 8, pl. 1,
figs 1-1, 1-2, 2-1, 2-2, 3-1, 3-2, 4-1, 4-2, 5-1, 5-2.
2012 Sphenolithus perpendicularis Shamrock, 2010 –Bown & Dunkley Jones: pl. 10, fig. 41.
2017 Sphenolithus perpendicularis Shamrock, 2010 –Bown & Newsam: pl. 11, figs 7–10, 13, non figs 11, 12.
Diagnosis: A large to very large sphenolith with a low tomoderate-height, cylindrical proximal element cycle. The
lower lateral cycle elements are thin. The upper lateralcycle elements are reduced in number to two, and are enlarged vertically and laterally to form two distally divergent spines, with an angle of ~90° between the spines. The
calcite c-axes in the upper lateral cycle elements are at anangle of ~45° to the median axis, so they are brightly birefringent in lateral view when the median axis is parallel
to one of the polarising axes, and dark when the medianaxis is at 45°. A small apical structure is present, whichappears to be monocyclic and monocrystalline. The topof the apical structure is level with the base of the inter-

Ultrastructure and taxonomy of the Sphenolithaceae

spine area between the two upper lateral element spines, or
projects slightly above it. Remarks: This is a very distinctive species with a very short range (within NP15, Middle
Eocene), making it an excellent biostratigraphic marker.
This is also the first species where the element count in theupper lateral element cycle is reduced to two elements––acritical step in the formation of the bifid spine characteristic of most species of Furcatolithus.
Sphenolithus shamrockiae n. sp.
Pl. 2, figs 1–4
2010 Sphenolithus furcatolithoides Locker, 1967 – Shamrock: pl. 1, figs 7-1, 7-2, 8-1, 8-2.
2014 Sphenolithus furcatolithoides Locker, 1967 morphotype A – Agnini et al.: pl. 3, figs 2, 3.
Derivation of name: In honour of Dr Jamie Shamrock,who figured the holotype of this species as S. furcatolithoides in Shamrock (2010). Diagnosis: A sphenolithwith a low proximal element cycle, a thin lower lateralelement cycle, and a high to very high, bifurcated upper
lateral element cycle with two elements that form a bifid spine. A small, monocyclic apical structure is present,
which does not extend above the base of the bifurcationof the bifid spine. Remarks: The presence of an apicalstructure (clearly visible when the specimen is oriented
at 45° to the polarising axes as a small birefringent element above the birefringent elements of the lower lateral element cycle; see Shamrock, 2010, pl. 1, fig. 7-2)
distinguishes this species from the otherwise similar S.
furcatolithoides, the holotype of which completely lacks
an apical structure. The apical structure is small, so it isunclear whether it is monocrystalline or a monocyclic
composite. This is the first sphenolithid species known tohave a bifid spine. Holotype: Shamrock (2010, pl. 1, figs
7-1, 7-2). Holotype height: 7.5 µm. Paratype: Shamrock(2010, pl. 1, figs 8-1, 8-2). Sample ODP-122-762C-15-2,
125–126 cm. Type locality: ODP Leg 122, Hole 762C,
Exmouth Plateau, offshore western Australia, southeastern
Indian Ocean. Type level: ODP-122-762C-15X-1, 48–49
cm; NP15b (of Martini, 1971)/CP13b (of Okada & Bukry,
1980), Middle Eocene (Lutetian), according to Shamrock (2010). Occurrence: The range of this species has
not been fully established because most previous studies
have not distinguished it from the similar, and closely re-53

lated, S. furcatolithoides. Agnini et al. (2014) separated S.
shamrockiae (as S. furcatolithoides morphotype A) from
S. furcatolithoides (as S. furcatolithoides morphotype B),
finding it restricted to their zone CNE10 (= middle NP15).
Sphenolithus furcatolithoides Locker, 1967 emend.
Pl. 2, figs 5, 6
1967 Sphenolithus furcatolithoides Locker: p. 363, pl. 1,
figs 14–16, text-figs 7, 8.
2005a Sphenolithus furcatolithoides Locker, 1967 –Bown: pl. 45, figs 1–3.
2014 Sphenolithus furcatolithoides Locker, 1967 morphotype B – Agnini et al.: pl. 3, figs 11, 12.
Emended diagnosis: A sphenolith with a low proximal
element cycle, a thin lower lateral element cycle, and ahigh to very high upper lateral element cycle. The upper
lateral element cycle has two vertically adjoined elements,
which bifurcate distally, forming a bifid spine. The point at
which the bifid spine bifurcates is approximately one-thirdfrom the base of the spine. Thin distal and lateral extensions of the two vertical elements of the bifid spine may
or may not be present, but if present, can vary greatly inlength. No apical structure is present. Remarks: The photomicrographs of the holotype (Locker, 1967, figs 14, 15)of S. furcatolithoides are over-exposed, making it difficult
to determine whether a lower lateral element cycle is present, although Locker’s sketches of the holotype (figs 7, 8)
strongly suggest that it is. Most subsequent illustrations of
this species clearly show the presence of a lower lateralelement cycle (e.g. Bown, 2005a, pl. 45, figs 1, 2). The
holotype clearly lacks any apical structure. The high, bifurcated upper lateral element cycle in S. furcatolithoides
and the closely related S. shamrockiae n. sp., formed fromthe high upper lateral element cycle of S. perpendicularis,and mark the evolution of the bifid spine, which is a key
structural component of subsequent species in the genus
Furcatolithus.
Sphenolithus labradorensis Firth, 1989 stat. nov.
Pl. 2, figs 7–10
1989 Sphenolithus furcatolithoides Locker, 1967 subsp.
labradorensis Firth: p. 277, pl. 2, figs 15, 16; pl. 3,
figs 1–4.

54

Howe

2006 Sphenolithus strigosus Bown & Dunkley Jones: p.
23, pl. 8, figs 6–15.
2006 Sphenolithus runus Bown & Dunkley Jones: p. 23,
pl. 8, figs 16–24.
2012 Sphenolithus strigosus Bown & Dunkley Jones,
2006 – Bown & Dunkley Jones: pl. 10, figs 44, 45.
2014 Sphenolithus labradorensis (Firth, 1989) Aubry: pp.
150, 282 (invalid, see remarks below).
2017 Sphenolithus runus Bown & Dunkley Jones, 2006 –Bown & Newsam: pl. 11, figs 30–35.
2017 Sphenolithus strigosus Bown & Dunkley Jones,
2006 – Bown & Newsam: pl. 11, figs 27–29.
Basionym: Sphenolithus furcatolithoides Locker, 1967
subsp. labradorensis Firth, 1989, p. 277, pl. 2, figs 15,
16; pl. 3, figs 1–4. Firth, J.V. 1989. Eocene and Oligocene calcareous nannofossils from the Labrador Sea, ODP
Leg 105. Proceedings of the ODP, Scientific Results, 105:
263–286. Diagnosis: A sphenolith with a low proximal
element cycle, a thin lower lateral element cycle, and ahigh upper lateral element cycle. The upper lateral element
cycle is reduced to two vertical elements, which bifurcate
distally. Thin distal extensions of these vertical elements
may or may not be present. No apical structure is present. Remarks: The change in status by Aubry (2014) isinvalid under ICN Art. 41.6 because, whilst the basionym
was cited, as required under Art. 41.5, the page and figure
numbers of the description of S. furcatolithoides subsp.
labradorensis by Firth were entirely omitted, which is not
permitted under ICN Art. 41.6. This species is likely theimmediate ancestor to Furcatolithus cuniculus n. comb.,with the main difference being the presence of a lower lateral element cycle in S. labradorensis, which is lost in thetransition to F. cuniculus. The presence or absence of alower lateral element cycle is the key structural difference
between the two species and the two genera.
The holotype of S. strigosus is very similar to that ofS. labradorensis, with both specimens clearly showing thepresence of a lower lateral element cycle and a bifid spine,
so S. strigosus is considered here to be a junior synonymof S. labradorensis. The holotype of S. runus is similarin size and overall appearance to the holotypes of both S.
labradorensis and S. strigosus, with a clearly visible lower
lateral element cycle, but no visible apical structure. The
bifid spine of the holotype (Bown & Dunkley Jones, 2006,
pl. 8, figs 18–20) is dark at 0° and bright at 45°, which is

opposite to the extinction pattern for the bifid spine of theholotype specimen of S. labradorensis. A suture can beseen surrounding the periphery of the spine, which here
is interpreted as the median suture of the bifid spine, ata low oblique angle to the plane of the slide. The otherspecimens of S. runus figured in Bown & Dunkley Jones(2006, pl. 8, figs 16, 17, 21–24) show a similar pattern, as
do the specimens of S. runus figured by Bown & Newsam(2017, pl. 11, figs 30, 31, 34, 35). The specimen figured as
S. runus by Bown & Newsam (2017, pl. 11, figs 32, 33)
has a bifid spine that is partially bright in both the 0° and
45° orientations to the polarising axes, and has a clearlyvisible median suture (their pl. 11, fig. 32), where the specimen is oriented at 0° to the polariser, so this specimen isconsidered to be specimen of S. labradorensis, even by
their criteria.
For these reasons, the holotype of S. runus is interpreted here as being a specimen of S. labradorensis oriented
with the median suture of the bifid spine lying parallel, or
slightly oblique, to the plane of the slide, rather than orthogonal to the plane of the slide, as in the holotype imageof S. labradorensis, and in which orientation the mediansuture of the bifid spine is visible. Accordingly, S. runus
is interpreted to be a junior synonym of S. labradorensis.
Sphenolithus dissimilis GroupThe species in this group all have medium-high to high,cylindrical to slightly flaring proximal element cycles, thinlateral element cycles, and monocyclic composite apicalstructures with subparallel to divergent elements, resulting
in a cylindrical or biconical overall shape in some species.
In some species, the elements in the apical structure are
all similar in height, giving the apical structure a cylindrical appearance with a flat distal surface, which is notseen in any other group of sphenoliths. The species in thisgroup are discussed below in approximate order of firststratigraphic appearance: S. truaxii, S. procerus, S. capricornutus, S. compactus, S. disbelemnos, S. multispinatus,
S. dissimilis and S. cometa. A range chart for this group ispresented in Figure 10.
Sphenolithus truaxii Bergen & de Kaenel in Bergen etal., 2017
Pl. 2, figs 11, 122017 Sphenolithus truaxii Bergen & de Kaenel in BergenUltrastructure and taxonomy of the Sphenolithaceae

et al.: p. 87, pl. 2, figs 21–26.

55

Sphenolithus procerus Maiorano & Monechi, 1997
Pl. 2, figs 13, 14

entiation of the upper lateral cycle elements from the two
apical elements is difficult in this species because the apical elements are at an angle of ~45° to the median axis,
so the c-axis orientations of the elements in the spines are
similar to the c-axis orientations of the elements in the upper lateral element cycle, and hence their birefringence issimilar. Close examination of most published images of
specimens where the median axis is parallel to one of thepolarising axes (e.g. Denne, 2007, pl. 1, fig. 14; Bergen etal., 2017, pl. 7, figs 26, 28, 30; Gennari et al., 2017, fig.
9a) shows that the upper lateral cycle elements are slightly
brighter than the two apical elements, and can be recognised as ultrastructurally distinct. Differentiation: This
species is superficially similar to the Eocene S. perpendicularis, although it is phylogenetically and ultrastructurally
unrelated, as the divergent spines in S. perpendicularis areelongated upper lateral cycle elements, and not elongatedapical structure elements, as seen in S. capricornutus.

1997 Sphenolithus procerus Maiorano & Monechi: p. 103,
pl. 1, figs 1–3.

Sphenolithus compactus Backman, 1980
Pl. 2, figs 17, 18

Diagnosis: A medium-sized sphenolith with a mediumhigh, slightly flared proximal element cycle. The lower
and upper lateral element cycles are slightly thickened.
The composite apical structure is monocyclic and cylindrical, with a relatively flat distal surface. Remarks: This
species resembles S. truaxii but differs in having a lower
proximal element cycle.

1980 Sphenolithus compactus Backman: p. 59, pl. 3, fig.
20.
2017 Sphenolithus paratintinnabulum Bergen & de Kaenel in Bergen et al.: p. 88, pl. 3, figs 29, 30; pl. 4, figs
1–6.

Diagnosis: A large sphenolith with a medium to tall cylindrical proximal element cycle. The elements of the lower
and upper lateral cycles are thick and extend laterallyslightly beyond the top of the proximal cycle, giving thelateral profile a slightly stepped appearance. The composite apical structure is monocyclic and cylindrical with agently convex to flat distal surface. The apical structure
is tall. Remarks: Under the LM, some specimens of thisspecies present an unusual appearance where the proximal
element cycle and the apical structure are approximately
equal in size and shape. In specimens like this, the proximal cycle and the apical structure can be difficult to distinguish.

Sphenolithus capricornutus Bukry & Percival, 1971
Pl. 2, figs 15, 16
1971 Sphenolithus capricornutus Bukry & Percival: p.
140, pl. 6, figs 4–6.
2007 Sphenolithus capricornutus Bukry & Percival, 1971
– Denne: pl. 1, fig. 14.
Diagnosis: A large to very large sphenolith with a medium-high to high, slightly to moderately flared proximal element cycle. The lower lateral cycle elements are thin, andthe upper lateral cycle elements are thick. The high apicalstructure is monocyclic and composite, and comprises two
prominent apical elements that diverge distally and laterally. Remarks: Such a pair of divergent apical elements
is not found in any other post-Eocene sphenolith. Differ-

Diagnosis: A very small to small sphenolith with a high,cylindrical proximal element cycle. The lateral element
cycles are thin. The composite apical structure is domed
and low. It is unclear whether the apical structure is monoor polycyclic. Remarks: The holotype of S. compactus
was described by Backman (1980) from NN3, in the Early
Miocene, and falls within the range described by Bergen etal. (2017) for S. paratintinnabulum, the holotype of which
was described from NN2, but which ranges up to the
middle of NN3, to 18.612Ma (Bergen et al., 2017, 2019a).
The holotypes of the two species are very similar, withrelatively tall, cylindrical proximal element cycles andlow apical structures, so S. paratintinnabulum is regarded
here as a junior synonym of S. compactus. This species
has been regarded by many workers as a small variety ofS. primus or S. moriformis (e.g. Perch-Nielsen, 1985, pp.
522, 523), but its tall, cylindrical proximal cycle is quite
unlike the much lower and slightly flaring proximal cycle

56

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of S. moriformis.
Sphenolithus disbelemnos Fornaciari & Rio, 1996
Pl. 2, figs 19, 20
1996 Sphenolithus disbelemnos Fornaciari & Rio: pl. 2,
figs 7–10; pl. 3, figs 19, 20; pl. 4, fig. 2.
1996 Sphenolithus aubryae de Kaenel & Villa: p. 128, pl.
11, figs 16–18.
2017 Sphenolithus disbelemnos Fornaciari & Rio, 1996 –Bergen et al.: pl. 3, figs 11–28.
Diagnosis: A small sphenolith with a tall, cylindrical proximal element cycle. The elements of the lower and upper
lateral cycles are thick, and extend laterally slightly beyond the top of the proximal cycle, giving the lateral profile a slightly stepped appearance. The composite apicalstructure is monocyclic and cylindrical, with a relatively
flat distal surface. The apical structure is low in height.
Remarks: The holotype of S. aubryae is very similar tothat of S. disbelemnos, other than being slightly larger (theholotype of S. disbelemnos is 2.95 µm high, that of S. aubryae 4.1 µm high), so S. aubryae is considered to be ajunior synonym of S. disbelemnos.

Sphenolithus multispinatus Maiorano & Monechi, 1997
Pl. 2, figs 21, 22
1997 Sphenolithus multispinatus Maiorano & Monechi:
pl. 1, figs 14–16.
2017 Sphenolithus multispinatus Maiorano & Monechi,
1997 – Bergen et al.: pl. 7, figs 14–17.
Diagnosis: A large sphenolith with a low, moderately flaring proximal element cycle, and relatively thick lateral element cycles. The apical structure is composite and monocyclic, with distally and laterally diverging elements,
resulting in an overall biconical shape. The elements in theapical structure are variable in length, so in lateral view,the distal surface of the apical structure appears uneven.
Remarks: The degree of divergence of the elements in theapical structure is greater in S. multispinatus than in S. cometa, and the elements are coarser.

Sphenolithus dissimilis Bukry & Percival, 1971
Pl. 2, figs 23–26
1971 Sphenolithus dissimilis Bukry & Percival, pl. 6, figs
7, 9, non fig. 8.
2017 Sphenolithus dissimilis Bukry & Percival, 1971 –Bergen et al.: pl. 3, figs 7–10.
Diagnosis: A large sphenolith with a tall, cylindrical proximal element cycle, slightly thickened lower and upper
lateral element cycles, and a moderately tall, monocyclic
composite apical structure that is cylindrical in shape. The
distal surface of the apical structure appears flat in lateralview. Remarks: This species has a similar range to S. disbelemnos, with which it appears to form a plexus in which
the height of the apical structure is variable––low in S.
disbelemnos, moderately high in S. dissimilis.
Sphenolithus cometa de Kaenel & Villa, 1996
Pl. 2, figs 27, 28
1996 Sphenolithus cometa de Kaenel & Villa: pl. 11, figs
22–24.
2017 Sphenolithus cometa de Kaenel & Villa, 1996 – Bergen et al.: pl. 7, figs 18–25.
Diagnosis: A medium-sized sphenolith with a tall, slightly
flaring to cylindrical proximal element cycle. The lower
and upper lateral element cycles are thin. The apical structure is monocyclic, tall, and has distally diverging elementsthat give this species an overall biconical shape. The distal
surface of the apical structure appears flat in lateral view.
Remarks: The divergent apical structure of this species isclearly different to the cylindrical apical structure of theotherwise similar S. dissimilis.
Sphenolithus conicus GroupThe species in this group are all medium-high to high,conical, with a medium-high to high, sharply pointed torounded, monocyclic apical structure. As with the S. anarrhopus group, the apical structures in most specimens ofspecies in this group are monocrystalline, but occasionally(particularly in S. conicus), it can be seen that the apicalstructure is monocyclic and composite, comprising several
elements, but with one or two larger elements dominating
the spine. The species in this group are discussed below

Ultrastructure and taxonomy of the Sphenolithaceae

in approximate order of first stratigraphic appearance: S.
conicus, S. calyculus, S. macroacanthos, S. pseudoheteromorphus, S. heteromorphus, S. preasii and S. milanetti. A
range chart for this group is presented in Figure 8.
Sphenolithus conicus Bukry, 1971aPl. 2, figs 29, 30
1971a Sphenolithus conicus Bukry: p. 320, pl. 5, figs 10–12.
2012 Sphenolithus conicus Bukry, 1971a – Bown & Dunkley Jones: pl. 13, figs 13–18.
2017 Sphenolithus conicus Bukry, 1971a – Bergen et al.:pl. 5, figs 7–18.
Diagnosis: A large sphenolith with a medium-high, moderately flaring proximal element cycle, thin lower and upper lateral element cycles, and a medium-high, rounded,
conical, monocyclic composite apical structure, usually
dominated by one or two large, sub-vertical elements.
Some specimens have a fully monocrystalline apical structure. Remarks: The transition from a monocyclic composite spine to a monocrystalline spine occurs in this species. These two morphotypes could be split into different
species. This is considered impractical here because it canbe very difficult to distinguish between a composite apicalstructure with a few coarse elements and a monocrystalline apical structure. All subsequent species in this lineage
have monocrystalline apical structures, although S. pseudoheteromorphus can have a cycle of small, thin apicalelements at the base of the large monocrystalline spine,
resulting in a composite apical structure.
Sphenolithus calyculus Bukry, 1985
Pl. 3, figs 1, 2
1985 Sphenolithus calyculus Bukry: p. 600, pl. 1, figs
13–19.
2017 Sphenolithus calyculus Bukry, 1985 – Bergen et al.:pl. 5, figs 1–4, non figs 5, 6.
Diagnosis: A medium-sized sphenolith with a mediumhigh proximal cycle, thin lower and upper lateral element
cycles, and a tall, narrow, conical monocrystalline apicalstructure. Remarks: This species is transitional between
S. conicus and S. pseudoheteromorphus. It is distinguished57

from both of these species by its taller and thinner apicalstructure, which is symmetrical, in contrast to the spine in
S. pseudoheteromorphus.
Sphenolithus macroacanthos Aubry, 2014
Pl. 3, figs 3, 4
non 1980 Sphenolithus elongatus Perch-Nielsen: p. 2, pl.
1, figs 14, 15; pl. 2, figs 5–11 (not considered here to
be a true sphenolithid).
1986 Sphenolithus elongatus Martini: p. 753, pl. 2, figs
7, 8 (homonym of S. elongatus Perch-Nielsen, 1980).
2014 Sphenolithus macroacanthos Aubry: pp. 150, 346,
nom. nov. pro Sphenolithus elongatus Martini, 1986.
2017 Sphenolithus calyculus Bukry, 1985 – Bergen et al.:pl. 5, figs 5, 6, non figs 1–4.
Diagnosis: A large to very large sphenolith with a medium-high proximal cycle, thin lower and upper lateralelement cycles, and a tall, narrow monocrystalline apical structure. Remarks: Sphenolithus elongatus Martini,
1986 is a homonym of S. elongatus Perch-Nielsen, 1980.
Aubry (2014) erected the name S. macroacanthos as a nomen novum for S. elongatus Martini, 1986. Sphenolithus
elongatus Perch-Nielsen, 1980 is not considered to be atrue sphenolithid, as the holotype does not appear to havea sphenolithid proximal cycle, and hence does not belong
to the family Sphenolithaceae. The holotype of S. elongatus Martini, 1986 is 9.6 µm high, while that of S. calyculus
is 5.0 µm. Otherwise the two species are very similar.
Sphenolithus pseudoheteromorphus Fornaciari & Agnini, 2009
Pl. 3, figs 5, 6
2009 Sphenolithus pseudoheteromorphus Fornaciari &Agnini: p. 97, pl. 1, figs 1–16; pl. 2, figs 1–5, 9, 13.
2017 Sphenolithus pseudoheteromorphus Fornaciari &Agnini, 2009 – Bergen et al.: pl. 7, figs 1–5.
Diagnosis: A very large sphenolith with a low, moderately
flared proximal element cycle, thin lower and upper lateralelement cycles, and a tall, pointed-conical monocrystalline apical structure that is usually at a slight angle to themedian axis of the sphenolith. A cycle of small apical elements may be present around the base of the apical struc-

58

Howe

ture. Remarks: This species is generally taller and thinneroverall than the closely related S. heteromorphus. The two
species can be separated by the inclination of the apicalstructure in S. pseudoheteromorphus.
Sphenolithus heteromorphus Deflandre, 1953
Pl. 3, figs 7, 8
1953 Sphenolithus heteromorphus Deflandre: p. 1786, pl.
1, figs 1–2.
2017 Sphenolithus heteromorphus Deflandre, 1953 – Bergen et al.: pl. 7, figs 6–11.
Diagnosis: A large to very large sphenolith with a low,
moderately flared proximal element cycle, slightly thickened lower and upper lateral element cycles, and a tall,pointed monocrystalline apical structure. Remarks: Sphenolithus heteromorphus can be very common in CN3 (ofOkada &Bukry, 1980)/NN4 (of Martini, 1971) in the Burdigalian, where it is an excellent marker species.
Sphenolithus preasii Bergen & de Kaenel in Bergen etal., 2017
Pl. 3, figs 9, 102017 Sphenolithus preasii Bergen & de Kaenel in Bergen
et al.: p. 90, pl. 5, figs 19–30.
Diagnosis: A very large sphenolith with a medium-high,moderately flared proximal element cycle, thickened lower and upper lateral element cycles, and a medium-high,pointed apical structure. In lateral view, the elements ofthe proximal cycle are slightly curved. Remarks: As noted by Bergen et al. (2017), S. preasii is transitional between S. conicus and S. milanetti, with the elements in theproximal cycle being slightly curved in lateral view, rather
than strongly curved, as in S. milanetti. The holotype of S.
preasii has a monocrystalline apical structure, in contrast
to the monocyclic composite apical structure of S. conicus, which is usually dominated by one or two large subvertical elements.
Sphenolithus milanetti Maiorano & Monechi, 1998
Pl. 3, figs 11, 12
1989 Sphenolithus sp. 1 Olafsson: p. 19, pl. 1, fig. 6.

1990 Sphenolithus milanetti Fornaciari & Rio in Fornaciari et al. (nomen nudum): pl. 3, figs 6A–D.
1998 Sphenolithus milanetti Maiorano & Monechi: pl. II,
figs 30, 31.
2016 Sphenolithus pospichalii Jiang et al.: p. 61, pl. 1, figs
1–8.
2017 Sphenolithus milanetti Maiorano & Monechi, 1998 –Bergen et al.: pl. 8, figs 1–9.
Diagnosis: A large to very large sphenolith with a highproximal element cycle. In lateral view, the elements ofthe proximal cycle are distinctly curved, resulting in astrongly concave proximal surface. The lower and upper
lateral element cycles are slightly thickened, and the apicalstructure is monocrystalline and moderate in height. Remarks: This species is superficially similar to the Eocene
S. orphanknollensis, as both species have high proximal
element cycles, with elements that are strongly curved inlateral view. Sphenolithus pospichalii was described ashaving a taller apical structure than S. milanetti; however,the difference in the height of the apical structure between
the two holotypes is minimal. As noted by Bergen et al.
(2017), the two holotypes are both 8 µm in height, andboth species were described from NN4, so they are here
considered synonymous.
Sphenolithus delphix GroupThe species in this group all have a flared proximal element cycle. The apical structure is monocyclic, composite
in S. bipedis and monocrystalline in S. spinula, S. microdelphix, S. delphix, S. tintinnabulum and S. belemnos. Species in this group are discussed below in approximate order of first stratigraphic appearance: S. bipedis, S. spinula,
S. microdelphix, S. delphix, S. tintinnabulum and S. belemnos. A range chart for this group is presented in Figure 10.
Sphenolithus bipedis Bergen & de Kaenel in Bergen etal., 2017
Pl. 3, figs 13, 142017 Sphenolithus bipedis Bergen & de Kaenel in Bergen
et al.: p. 83, pl. 1, figs 5–12.
Diagnosis: A small sphenolith with a medium-high,strongly flared proximal element cycle. The lateral element cycles are thin, and there is a low, conical mono-

Ultrastructure and taxonomy of the Sphenolithaceae

cyclic composite apical structure. Remarks: This species
resembles S. neoabies in having a strongly flared proximal
element cycle and a low apical structure, but is older, andhas a disjunct range (Bergen et al., 2017).
Sphenolithus spinula Bergen & de Kaenel in Bergen etal., 2017
Pl. 3, figs 15, 16
2017 Sphenolithus spinula Bergen & de Kaenel in Bergen
et al.: p. 91, pl. 6, figs 1–8.
Diagnosis: A medium-sized sphenolith with a tall, strongly flared proximal element cycle. The lower and upper
lateral element cycles are thin, and the monocrystalline
apical structure is medium-high. Remarks: Sphenolithus
spinula is distinguished from the otherwise similar S. microdelphix in having a taller, but equally strongly flared
proximal element cycle.
Sphenolithus microdelphix Bergen & de Kaenel in Bergen et al., 2017
Pl. 3, figs 17, 18
2017 Sphenolithus microdelphix Bergen & de Kaenel inBergen et al.: p. 91, pl. 6, figs 21–25.
2017 Sphenolithus delphix Bukry, 1973 – Gennari et al.:figs 9m, n, non figs 9i–l.
Diagnosis: A medium-sized sphenolith with a mediumhigh, strongly flared proximal element cycle, a thin lower
lateral element cycle, a slightly thickened upper lateralelement cycle, and a tall, conical apical structure. In wellpreserved specimens, two horizontally opposite elementsin the proximal cycle are proximally and laterally extended, with lengths similar to the height of the apical structure. Remarks: The holotype of S. microdelphix clearlyshows an extended element in the proximal cycle (Bergen
et al., 2017, pl. 6, figs 11, 12, on the right-hand side of thespecimen). See remarks for S. delphix.
Sphenolithus delphix Bukry, 1973
Pl. 3, figs 19–22
1973 Sphenolithus delphix Bukry: pl. 3, figs 19–22.
1974 Sphenolithus sp. 1 Müller, pl. 4, figs 3–6.

59

1974 Sphenolithus sp. 2 Müller, pl. 4, figs 7, 8.
1986 Sphenolithus delphix Bukry, 1973 – Knüttel: pl. 4,
figs 1–5, 8.
1989 Sphenolithus delphix Bukry, 1973 – Firth: pl. 4, figs
7, 8.
2017 Sphenolithus delphix Bukry, 1973 – Bergen et al.: pl.
6, figs 21–25.
2017 Sphenolithus delphix Bukry, 1973 – Gennari et al.:figs 9i–n.
Diagnosis: A large sphenolith with a medium-high,strongly flared proximal element cycle, a thin lower lateralelement cycle, a slightly thickened upper lateral element
cycle, and a tall, conical, monocrystalline apical structure. In well-preserved specimens, two horizontally opposite elements in the proximal cycle are proximally andlaterally extended, to a variable degree. Remarks: Most
descriptions of S. delphix emphasise the strongly flared
proximal element cycle as characteristic of this species.
Published images of this species show a wide range ofvariation in the degree of flare of the proximal cycle, withsome images showing the length of the elements in theproximal cycle being approximately equal to the length of
the apical structure. The type description by Bukry (1973)
clearly mentioned that “The apical spine and two of thebasal spines are slender and elongate, resulting in a triradiate outline”, and in the remarks, Bukry commented that
“The structure of some specimens suggests that the twolong basal spines are secondary elongations. Because of
the regular position of these spines and the low abundanceof S. delphix in populations of fossil coccoliths, however,these structures are probably biologic in origin”.
Close examination of the LM images of the holotype(Bukry, 1973, pl. 3, figs 19, 21, 22) show a difference inthe lengths of the proximal cycle elements between his fig.
19 (a transmitted light image) and fig. 20 (a cross-polarised-light image), which is interpreted here as evidence
that the holotype specimen bears extended elements in theproximal cycle, which are about half the height of the apical structure in length. The specimen figured here in Plate3, figs 21 and 22, shows an extended proximal cycle element on the right-hand side of the proximal cycle, which
is similar in length to the apical structure. This extensionof some of the proximal cycle elements is a structural innovation not shown by any sphenolithid other than theclosely related S. microdelphix, which is smaller, with a

60

Howe

proportionally shorter apical structure, but is otherwise
very similar.
It is clear from the SEM images of Müller (1974, pl.
4, figs 7, 8) and Knüttel (1986, pl. 4, figs 1, 2), and theLM images of Firth (1989, pl. 4, figs 7, 8) that these horizontally opposed proximal cycle elements can be extended
in length, elongating into long spines, similar in length tothe apical structure. This form was described, but not figured, as a “long triradiated” S. delphix by de Kaenel &Villa (1996, p. 99), who mentioned that “Moreover, a very
short, characteristic interval contains abundant forms oflarge S. delphix. This ‘triradiated’ form possesses a very
long apical spine and two extremely elongated proximal
elements, and it occurs near the top of the range of S. delphix, together with frequent T. carinatus”.
Sphenolithus tintinnabulum Maiorano & Monechi, 1997
Pl. 3, figs 23, 24
1997 Sphenolithus tintinnabulum Maiorano & Monechi:
p. 104, pl. 1, figs 4–6.
2017 Sphenolithus tintinnabulum Bergen et al.: pl. 4, figs
7–18.
Diagnosis: A small sphenolith with a moderately high,moderately flared proximal element cycle, thin lower andupper lateral element cycles, and a low monocrystalline
apical structure that is conical in shape. Remarks: See remarks for S. belemnos.
Sphenolithus belemnos Bramlette & Wilcoxon, 1967
Pl. 3, figs 25–28
1967 Sphenolithus belemnos Bramlette & Wilcoxon: p.
118, pl. 2, figs 1–3.
2017 Sphenolithus belemnos Bramlette & Wilcoxon, 1967
– Bergen et al.: pl. 4, figs 19–30.
Diagnosis: A large sphenolith with a moderately tall,slightly flaring proximal element cycle. Both the lower
and upper lateral element cycles are thin. The monocrystalline apical structure is tall and conical. Remarks: The
proximal element cycle of S. belemnos is taller than that ofS. tintinnabulum, but is not as flared. It is similar in heightto that of S. disbelemnos, but is more flared. The apicalstructure of S. belemnos is monocrystalline, like that of S.

tintinnabulum (and unlike the monocyclic composite apical structure of S. disbelemnos), so, overall, S. belemnos
is considered here to be likely descended from S. tintinnabulum, although it could also be descended from S. disbelemnos.
Sphenolithus quadrispinatus GroupThe single species in this group has a low to medium-high,cylindrical proximal element cycle. The apical structure ismonocyclic, with usually four elements bearing thin extensions that extend laterally and vertically. A range chart
for the single species in this group is presented in Figure 8.
Sphenolithus quadrispinatus Perch-Nielsen, 1980
1980 Sphenolithus quadrispinatus Perch-Nielsen: p. 3, pl.
1, figs 11, 13; pl. 2, figs 1–4.
Diagnosis: A large to very large sphenolith with a low to
medium-high, cylindrical proximal element cycle, thinlateral element cycles, and a monocyclic apical structurewith usually four elements bearing thin extensions that extend laterally and vertically. Remarks: This species is apartial homeomorph of species in the S. dissimilis group––
particularly S. capricornutus and S. multispinatus––withwhich it shares an apical structure with distally and laterally diverging elements. The EM images of this species
in Perch-Nielsen (1980, pl. 2, figs 1–4) are of high quality and show multiple well-preserved specimens. It seems
clear from these images that this species is distinct from
species of the S. dissimilis group.
Sphenolithus quadrispinatus has a short range in the
Tortonian, and has very rarely been recorded. The only record in the International Ocean Discovery Program SEDIS
database of DSDP, ODP and IODP data is that of Quinterno (1994) who recorded it from CN8 (of Okada & Bukry,
1980) in ODP Hole 841B, from the Tonga Trench in the
Pacific Ocean, but did not present any images.
Genus Furcatolithus Martini, 1965 emend.
Emended diagnosis: Conical coccoliths with a proximal element cycle of radially arranged elements. Above
the proximal element cycle, there is usually a verticallysplit bifid spine, composed of two vertical elements. The
two elements of the bifid spine often bear thin extensions

Ultrastructure and taxonomy of the Sphenolithaceae

that extend distally and laterally. No lower lateral element cycle, or apical structure (apical cycle or spine), as
seen in species of the genus Sphenolithus, is ever present. Type species: Furcatolithus distentus Martini, 1965.
Synonym: Pseudozygrhablithus Haq, 1971. Discussion:
Martini (1965) described F. distentus as the generotype of
Furcatolithus. The holotype (Martini, 1965, figs 8, 9) is an
isolated bifid spine, with thin distal extensions. No proximal cycle is present; it is interpreted here as having broken
off. The holotype was interpreted by Martini (1965) to beof Miocene age (Catapsydrax dissimilis planktonic foraminiferal zone). As F. distentus has been reported in subsequent works by many authors (e.g. Perch-Nielsen, 1985;
Bown & Dunkley Jones, 2012) to be of mid-Oligocene
age, the age interpretation of Martini (1965) is considerederroneous. Bramlette & Wilcoxon (1967) examined material from the same core that Martini (1965) described
F. distentus from, and figured specimens (Bramlette &Wilcoxon, 1967, pl. 1, fig. 5; pl. 2, figs 4, 5) that clearlyshow the presence of a proximal element cycle (which
they termed ‘short basal spines’), the absence of a lower
lateral element cycle, and the absence of an apical element
cycle or spine. They commented that “The apical spine iseasily separated from the short basal spines, particularly inthe poorly preserved specimens of some samples”, which
seems to be a reference to the fact that Martini’s (1965)
holotype has a missing proximal element cycle. They considered the core examined by Martini (1965) to belong to
the upper Globigerina ampliapertura or lower Globorotalia opima opima planktonic foraminiferal zones, supporting a mid-Oligocene range for F. distentus.
Bramlette & Wilcoxon (1967) recombined F. distentus
into the genus Sphenolithus Deflandre, 1952, presumably
because of the overall similarity of the forms (i.e. conicalgross morphology) between the generotype of Sphenolithus (S. radians Deflandre, 1952) and F. distentus. Curiously, Bramlette & Wilcoxon (1967) did not attempt tojustify or discuss their recombination at all, instead confining their discussion to the ultrastructure of F. distentus,
and its geographical and stratigraphical distribution. Their
recombination has been followed by almost all nannofossil workers, having the effect of completely suppressing
the genus Furcatolithus. This recombination is rejected
here, due to the major structural differences between thegenerotypes of the two genera––the presence of a bifid
spine and the absence of a lower lateral element cycle and61

any apical structure in F. distentus, and the presence oflower and upper lateral element cycles and an apical structure in S. radians, which lacks a bifid spine.
Furcatolithus is interpreted to have evolved from theS. kempii group during the Middle Eocene. The lineage
from S. kempii to S. perpendicularis to S. shamrockiae to
S. furcatolithoides to S. labradorensis shows a trend of increasing height and decreasing element count in the upper
lateral element cycle––which became the two-part bifid
spine in Furcatolithus species––along with a reductionin height of the apical structure. The eventual complete
loss of the apical structure occurred in the transition from
S. furcatolithoides to S. labradorensis, and was followed
by loss of the lower lateral element cycle in the transition
from S. labradorensis to F. cuniculus––the oldest speciesof Furcatolithus. The bifid spine is reduced in size in the F.
triangularis group, and is ultimately lost completely in thelast representative of the genus––F. umbrellus.
Seventeen Furcatolithus species are recognised asvalid here. These species have been divided into three
informal groups of species, based on shared morphology.
These groups are listed in Table 2 and are detailed below,
with both groups and species in approximate order of firststratigraphical appearance.
Furcatolithus predistentus GroupThe species in this group all have high (>~65°) medianaxis/base bifid spine angles. Most species (e.g. F. predistentus) have low proximal cycles (~10–15% of the totalheight, excluding distal bifurcations), although some species (F. obtusus, F. peartiae and F. tawfikii) have higher
proximal cycles. The species in this group are discussed
below in approximate order of first stratigraphical appearance: F. cuniculus, F. predistentus, F. obtusus, F. celsus, F.
intercalaris, F. akropodus, F. tribulosus, F. peartiae and F.
tawfikii. A range chart for this group is presented in Figure
11. A selection of species from each group in the genus ispresented on Plate 4.
Furcatolithus cuniculus (Bown, 2005a) n. comb.
Pl. 4, figs 1–4
2005a Sphenolithus cuniculus Bown: p. 46, pl. 45, figs
6–10.
Basionym: Sphenolithus cuniculus Bown, 2005a, p. 46,

62

Howe

pl. 45, figs 6–10. Bown, P.R. 2005a. Palaeogene calcareous nannofossils from the Kilwa and Lindi areas of coastal
Tanzania (Tanzania Drilling Project 2003–4). Journal of
Nannoplankton Research, 27(1): 21–95. Diagnosis: A medium to large furcatolith with a high, blocky bifid spine,
and a low proximal element cycle. The tips of the bifid
spine bifurcate 30% of the way down the spine. The angle
between the median axis and the top of the proximal element cycle is approximately 90°. The base of the proximal element cycle is concave. Remarks: Bown (2005a)
described this species as being similar to (and possiblya preservational variant of) S. furcatolithoides, but withshorter lower quadrants (i.e. a lower proximal element
cycle) and broader upper quadrants (i.e. a broader bifid
spine). Unlike S. furcatolithoides, which has a lower lateral element cycle (a key characteristic of Sphenolithus,
as emended here), F. cuniculus completely lacks a lower
lateral element cycle, and so belongs to Furcatolithus.
Furcatolithus cuniculus has an unusually blocky bifid
spine, with thick vertical bifurcations, so measurement of
the total height is taken to the top of the bifurcations. For
the holotype, this results in the proximal cycle being 15%of the total height. F. cuniculus is the first species of thegenus to have evolved.

not be present, and if present, can vary greatly in length.
Remarks: See remarks for F. celsus below.
Furcatolithus obtusus (Bukry, 1971a) n. comb.
Pl. 4, figs 7–12
1971a Sphenolithus obtusus Bukry: p. 321, pl. 6, figs 1–9.
2005a Sphenolithus obtusus Bukry, 1971a – Bown, pl. 45,
figs 11–20.
Basionym: Sphenolithus obtusus Bukry, 1971a, p. 321, pl.
6, figs 1–9. Bukry, D. 1971a. Cenozoic Calcareous Nannofossils from the Pacific Ocean. Transactions of the San
Diego Society of Natural History, 16(14): 303–327. Diagnosis: A large furcatolith with a bifid spine, and a proximal
element cycle that is ~25% of the total height. The angle
between the median axis and the top of the proximal element cycle is ~50–60°. The base of the proximal element
cycle is concave. Thin distal extensions of the bifid spine
may or may not be present, and if present, can vary greatly
in length. Remarks: The precise relationships between theearliest forms of Furcatolithus are unclear. Either F. cuniculus or F. predistentus could be the ancestor of F. obtusus.
Furcatolithus celsus (Haq, 1971) n. comb.

Furcatolithus predistentus (Bramlette & Wilcoxon,
1967) n. comb.
Pl. 4, figs 5, 6
1967 Sphenolithus predistentus Bramlette & Wilcoxon: p.
126, pl. 1, fig. 6; pl. 2, figs 10, 11.
2012 Sphenolithus predistentus Bramlette & Wilcoxon,
1967 – Bown & Dunkley Jones: pl. 11, figs 17–22.
2017 Sphenolithus predistentus Bramlette & Wilcoxon,
1967 – Bergen et al.: pl. 11, figs 15, 17–20.
Basionym: Sphenolithus predistentus Bramlette & Wilcoxon, 1967, p. 126, pl. 1, fig. 6; pl. 2, figs 10, 11. Bramlette M.N. & Wilcoxon J.A. 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I.
Tulane Studies in Geology, 5(3): 93–131. Diagnosis: A
large furcatolith with a very low proximal element cyclethat is ~10% of the total height. The angle between the
median axis and the top of the proximal element cycle is~80–90°. The base of the proximal element cycle is concave. Thin distal extensions of the bifid spine may or may

1971 Sphenolithus celsus Haq: p. 121, pl. 1, figs 1–5; pl.
5, fig. 4.
2012 Sphenolithus celsus Haq, 1971 – Bown & Dunkley
Jones: pl. 11, figs 24–26.
2017 Sphenolithus celsus Haq, 1971 – Bergen et al.: pl.
11, figs 25–30.
Basionym: Sphenolithus celsus Haq, 1971, p. 121, pl. 1,
figs 1–5; pl. 5, fig. 4. Haq, B.U. 1971. Paleogene calcareous nannoflora. Parts I–IV. Stockholm Contributions inGeology, 25: 1–158. Diagnosis: A very large furcatolithwith a bifid spine and a very low proximal element cyclethat is ~10% of the total height. The total height is >9 µm.
The bifid spine narrows to become thin and parallel-sided
at about one-third of the total height of the spine. The angle
between the median axis and the top of the proximal element cycle is ~80–90°. The base of the proximal element
cycle is concave. Thin distal extensions of the bifid spine
may or may not be present, and if present, can vary greatly
in length. Remarks: The proximal element cycle and theUltrastructure and taxonomy of the Sphenolithaceae

lower part of the bifid spine are very similar to those of F.
predistentus, but the upper part of the bifid spine, where
it narrows to become parallel-sided (clearly visible in theholotype specimen in Haq, 1971, pl. 5, fig. 4), is different,
and provides a criterion for separating the two species.
Furcatolithus intercalaris (Martini, 1976) n. comb.
Pl. 4, figs 13, 14
1976 Sphenolithus intercalaris Martini: p. 395, pl. 6, fig.
9; pl. 13, figs 25, 26.
2012 Sphenolithus intercalaris Martini, 1976 – Bown &Dunkley Jones: pl. 11, fig. 13.
2015 Sphenolithus intercalaris Martini, 1976 – Fioroni etal.: pl. 2, figs 15, 16.
Basionym: Sphenolithus intercalaris Martini, 1976, p.
395, pl. 6, fig. 9; pl. 13, figs 25, 26. Martini, E. 1976.
Cretaceous to Recent calcareous nannoplankton from theCentral Pacific Ocean (DSDP Leg 33). Initial Reports of
the Deep Sea Drilling Project, 33: 383–423. Diagnosis: A
medium-sized furcatolith with a bifid spine and a proximal element cycle that is less than 5% of the total height.
The proximal cycle is often missing. The angle between
the median axis and the top of the proximal cycle is ~90°.
The lateral profile of the bifid spine is outwardly convex.
Thin distal extensions of the bifid spine may or may not
be present, and if present, can vary greatly in length. Remarks: The holotype of S. intercalaris Martini, 1976 is
an isolated bifid spine with the proximal cycle missing(much like the holotype of F. distentus Martini, 1965),
which is interpreted here as being a broken specimen. The
LM photograph by Fioroni et al. (2015, pl. 2, fig. 16) of F.
intercalaris clearly shows very small proximal cycle elements below the bifid spine. This species seems to be very
closely related to S. predistentus, as both species share avery low proximal element cycle with small elements, but
clearly differs in the lateral profile of the bifid spine, whichis strongly convex in S. intercalaris, and sub-linear in S.
predistentus.
Furcatolithus akropodus (de Kaenel & Villa, 1996) n.
comb.
Pl. 4, figs 15, 16
1990 Sphenolithus sp. 1 Fornaciari & Rio in Fornaciari et63al.: p. 238, pl. 2, figs 1–3.
1996 Sphenolithus akropodus de Kaenel & Villa: p. 127,
pl. 11, figs 1, 2, 4–11.
2012 Sphenolithus akropodus de Kaenel & Villa (1996) –Bown & Dunkley Jones: pl. 11, figs 29–38.
2017 Sphenolithus akropodus de Kaenel & Villa (1996) –Bergen et al.: pl. 10, figs 25–30; pl. 11, figs 1–4.
Basionym: Sphenolithus obtusus de Kaenel & Villa, 1996,
p. 127, pl. 11, figs 1, 2, 4–11. de Kaenel, E. & Villa, G.
1996. Oligocene-Miocene calcareous nannofossil biostratigraphy and paleoecology from the Iberia Abyssal Plain.
Proceedings of the Ocean Drilling Program, Scientific
Results, 149: 79–145. Diagnosis: A large to very large
furcatolith with a tall bifid spine and a proximal element
cycle that is ~15% of the total height. The angle between
the median axis and the top of the proximal element cycle
is >70°. The base of the proximal element cycle is concave. The tops of the elements in the proximal cycle are
distally convex. The lateral end of the proximal cycle elements can extend slightly beyond the base of the bifid
spine. Thin distal extensions of the bifid spine may or may
not be present, and if present, can vary greatly in length.
Remarks: The tall, linear-sided bifid spine of this species
is diagnostic. The likely ancestor is F. predistentus or F.
celsus.
Furcatolithus tribulosus (Roth, 1970) n. comb.
Pl. 4, figs 17, 18
1970 Sphenolithus tribulosus Roth: p. 870, pl. 14, figs 5,
7, 8.
2006 Sphenolithus tribulosus Roth, 1970 – Bown & Dunkley Jones: pl. 8, figs 1–5.
Basionym: Sphenolithus tribulosus Roth, 1970, p. 870,
pl. 14, figs 5, 7, 8. Roth P.H. 1970. Oligocene calcareous
nannoplankton biostratigraphy. Eclogae Geologicae Helvetiae, 63(3): 799–881. Diagnosis: A large furcatolith witha bifid spine and a very low proximal element cycle thatis <15% of the total height. The angle between the medianaxis and the top of the proximal element cycle is >80°. Thebase of the proximal element cycle is concave. Thin distal
extensions of the bifid spine may or may not be present,
and if present, can vary greatly in length. The base of thebifid spine is wider than in similar species (e.g. S. predis-

64

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tentus), such that the lateral profile of the spine is concave.
The bifid spine bears small serrate ridges, which are notoften visible under the LM. Remarks: This species wasvery well illustrated by Bown & Dunkley Jones (2006, pl.
8, figs 1–5). It seems to be closely related to both S. intercalaris and S. predistentus, but differs from them in the
concave lateral profile of the bifid spine.
Furcatolithus peartiae (Bown & Dunkley Jones, 2012
emend. Bergen & de Kaenel in Bergen et al., 2017) n.
comb.
Pl. 4, figs 19, 20
2012 Sphenolithus peartiae Bown & Dunkley Jones: p.
34, pl. 11, figs 39–44.
2017 Sphenolithus peartiae Bown & Dunkley Jones, 2012
emend. Bergen & de Kaenel in Bergen et al.: p. 98, pl.
11, figs 5–14.
Basionym: Sphenolithus peartiae Bown & Dunkley
Jones, 2012, p. 34, pl. 11, figs 39–44. Bown, P.R. &Dunkley Jones, T. 2012. Calcareous nannofossils fromthe Paleogene equatorial Pacific (IODP Expedition 320
Sites U1331–1334). Journal of Nannoplankton Research,
32(2): 3–51. Diagnosis: A large furcatolith with a bifid
spine and a proximal element cycle that is ~20–25% of
the total height. The angle between the median axis andthe top of the proximal element cycle is ~70°. The base of
the proximal element cycle is concave. Thin distal extensions of the bifid spine may or may not be present, and if
present, can vary greatly in length. The height of the bifid
spine is lower than in similar species (e.g. S. akropodus).

Remarks: This species is most similar to, and likely descended from, F. akropodus, but has a lower bifid spine.
Furcatolithus tawﬁkii (Bergen & de Kaenel in Bergen etal., 2017) n. comb.
2017 Sphenolithus tawfikii Bergen & de Kaenel in Bergen
et al.: p. 95, pl. 9, figs 17–20.
Basionym: Sphenolithus tawfikii Bergen & de Kaenel inBergen et al., 2017, p. 95, pl. 9, figs 17–20. Bergen, J., de
Kaenel, E., Blair, S., Boesiger, T. & Browning, E. 2017.
Oligocene–Pliocene taxonomy and stratigraphy of the genus Sphenolithus in the circum North Atlantic Basin: Gulf
of Mexico and ODP Leg 154. Journal of Nannoplankton
Research, 37(2–3): 77–112. Diagnosis: A large furcatolith with a bifid spine and a proximal element cycle thatis ~35–40% of the total height. The angle between the
median axis and the top of the proximal element cycle is~80°. The base of the proximal element cycle is linear at
the periphery and steeply concave in the centre. Thin distal
extensions of the bifid spine may or may not be present,
and if present, can vary greatly in length. Remarks: This
species has a taller proximal element cycle than any otherspecies in the F. predistentus group, but, like the othermembers of the group, it has a high angle between the median axis and the top of the proximal cycle.
Furcatolithus ciperoensis GroupSpecies in this group all have low (<~50°) median axis/
base bifid spine angles. The proximal cycles are high,~30–45% of the total height, excluding the distal bifurca-

Table 2: Species of Furcatolithus grouped into informal morphological groups, by approximate order of first stratigraphical appearance

PROXIMAL CYCLE
GROUP
F. predistentus

MORPHOLOGICAL CRITERIONHigh (>~65˚) median axis/base bifid spine angle

F. ciperoensis

Low (<~50˚) median axis/base bifid spine angle
High proximal cycle, ~30-45% of total height,
excluding distal bifurcations

F. triangularis

Very high proximal cycle, >60% of total height,
excluding distal bifurcations

RANGE
Middle Eocene–
Late Oligocene(Lutetian–Chattian)

SPECIESF. cuniculus
F. predistentus
F. obtusus
F. celsus
F. intercalaris
F. akropodus
F. tribulosus
F. peartiae
F. tawfikii
Oligocene
F. bulbulus(Rupelian–Chattian) F. distentus
F. ciperoensis
F. patifunditis
F. directus
Early Oligocene–
F. triangularis
Early Miocene
F. avis(Rupelian–Aquitanian) F. umbrellus

BIFID SPINE% OF TOTAL HEIGHTHEIGHT
20–25%
high
10%
high
20–25%
high
10%
high
<10%
high
15%
high
<15%
high
20–25%
medium35–40%
medium35%
medium30–35%
medium40%
medium40–45%
medium30–35%
medium60%
low>65%
very low>90%
very low to absent

MEDIAN AXIS/TOP OFPROXIMAL CYCLE ANGLE
90–100˚
80–90˚
60–65˚
80–90˚90˚
65–70˚
90–100˚
65–70˚80˚
45–50˚45˚40˚30˚30–35˚
40–50˚40˚n/aUltrastructure and taxonomy of the Sphenolithaceae

tions. Species in this group are discussed below in approximate order of first stratigraphic appearance: F. bulbulus,
F. distentus, F. ciperoensis, F. patifunditis and F. directus.
A range chart for this group is presented in Figure 11.
Furcatolithus bulbulus (Bergen & de Kaenel in Bergen
et al., 2017) n. comb.

65

or may not be present, and if present, can vary greatly inlength. Remarks: See discussion for the genus.
Furcatolithus ciperoensis (Bramlette & Wilcoxon, 1967)
n. comb.
Pl. 4, figs 23, 24

2017 Sphenolithus bulbulus Bergen & de Kaenel in Bergen et al.: p. 96, pl. 9, figs 25–30; pl. 10, figs 1–6.

1967 Sphenolithus ciperoensis Bramlette & Wilcoxon: p.
120, pl. 2, figs 15–20.
2017 Sphenolithus ciperoensis Bramlette & Wilcoxon,
1967 – Bergen et al.: pl. 9, figs 5–10.

Basionym: Sphenolithus bulbulus Bergen & de Kaenel inBergen et al., 2017, p. 96, pl. 9, figs 25–30; pl. 10, figs
1–6. Bergen, J., de Kaenel, E., Blair, S., Boesiger, T. &Browning, E. 2017. Oligocene–Pliocene taxonomy andstratigraphy of the genus Sphenolithus in the circum North
Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journalof Nannoplankton Research, 37(2–3): 77–112. Diagnosis:
A large furcatolith with a proximal element cycle that is~35% of the total height. The angle between the medianaxis and the top of the proximal element cycle is ~45°.
The base of the proximal element cycle is concave. The
lateral periphery of the proximal cycle elements is convex. Thin distal extensions of the bifid spine may or may
not be present, and if present, can vary greatly in length.
Remarks: The indented lateral profile of the entire furcatolith, and the convex lateral periphery of the proximal
cycle elements, distinguishes this species from the otherwise similar F. ciperoensis and F. patifunditis.

Basionym: Sphenolithus ciperoensis Bramlette & Wilcoxon, 1967, p. 120, pl. 2, figs 15–20. Bramlette, M.N. & Wilcoxon, J.A. 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W. I. Tulane Studies inGeology, 5(3): 93–131. Diagnosis: A large furcatolith witha proximal element cycle that is ~40% of the total height
and a moderately high bifid spine. The angle between the
median axis and the top of the proximal element cycle isapproximately 35–40°. The base of the proximal element
cycle is concave. The lateral periphery is linear. Thin distal
extensions of the bifid spine may or may not be present,
and if present, can vary greatly in length. Remarks: This
species is the most common furcatolith in Upper Oligocene assemblages. Furcatolithus bulbulus, F. patifunditis
and F. directus are all similar to F. ciperoensis, and all havecomparable ranges.

Furcatolithus distentus Martini, 1965
Pl. 4, figs 21, 22
1965 Furcatolithus distentus Martini: p. 407, pl. 35, figs
7–9.
1967 Sphenolithus distentus (Martini, 1965) Bramlette &Wilcoxon: pl. 1, fig. 5; pl. 2, figs 4, 5.
2017 Sphenolithus distentus (Martini, 1965) Bramlette &Wilcoxon – Bergen et al.: pl. 10, fig. 10.
Diagnosis: A large to very large furcatolith with a moderately high bifid spine, and a proximal element cycle that is~25–30% of the total height. The angle between the median axis and the top of the proximal element cycle is approximately 45°. The base of the proximal element cycle
is concave. Thin distal extensions of the bifid spine may

Furcatolithus patifunditus (Bergen & de Kaenel in Bergen et al., 2017) n. comb.
2017 Sphenolithus patifunditus Bergen & de Kaenel inBergen et al.: pl. 9, figs 9–16.
Basionym: Sphenolithus patifunditus Bergen & de Kaenel
in Bergen et al., 2017, p. 95, pl. 9, figs 9–16. Bergen, J., de
Kaenel, E., Blair, S., Boesiger, T. & Browning, E. 2017.
Oligocene–Pliocene taxonomy and stratigraphy of the genus Sphenolithus in the circum North Atlantic Basin: Gulf
of Mexico and ODP Leg 154. Journal of Nannoplankton
Research, 37(2–3): 77–112. Diagnosis: A medium-sized
furcatolith with a proximal element cycle that is ~40–45%
of the total height, and a medium-height bifid spine. The
angle between the median axis and the top of the proximal
element cycle is approximately 30°. The base of the proxi-

Howe
66

Figure 11: Range chart for the Furcatolithus predistentus, F. ciperoensis and F. triangularis
groups. Ranges based on Bergen et al. (2017), Bown & Dunkley-Jones (2012) and Aubry(2014). All measurements are based on the author’s measurements of the holotype or paratype
images. All sketches have been traced from holotype or paratype LM or SEM images

Ultrastructure and taxonomy of the Sphenolithaceae

mal element cycle is concave. Thin distal extensions of thebifid spine may or may not be present, and if present, canvary greatly in length. The lateral periphery is concave.
Remarks: This species is very similar to F. bulbulus, inthat both species have concave lateral peripheries, but F.
patifunditis lacks the convex lateral periphery of the elements in the proximal cycle of that species.
Furcatolithus directus (Bergen & de Kaenel in Bergen etal., 2017) n. comb.
2017 Sphenolithus directus Bergen & de Kaenel in Bergen
et al.: pl. 9, figs 21–24.
Basionym: Sphenolithus directus Bergen & de Kaenel inBergen et al., 2017, p. 96, pl. 9, figs 21–24. Bergen, J., de
Kaenel, E., Blair, S., Boesiger, T. & Browning, E. 2017.
Oligocene–Pliocene taxonomy and stratigraphy of the genus Sphenolithus in the circum North Atlantic Basin: Gulf
of Mexico and ODP Leg 154. Journal of Nannoplankton
Research, 37(2–3): 77–112. Diagnosis: A medium-sized
furcatolith with a proximal element cycle that is ~35%of the total height, and a medium-height bifid spine. The
angle between the median axis and the top of the proximal
element cycle is 30–35°. Thin distal extensions of the bifid
spine may or may not be present, and if present, can vary
greatly in length. The lateral periphery is slightly concave.
The proximal element cycle is less flared than similar species. Remarks: The main difference between this species
and F. ciperoensis is that the proximal element cycle isless flared.
Furcatolithus triangularis GroupSpecies in this group all have very high proximal cycles,>60% of the total height, excluding the distal bifurcations.
Species in this group are discussed below in approximate
order of first stratigraphic appearance: F. triangularis, F.
avis and F. umbrellus. A range chart for this group is presented in Figure 11.
Furcatolithus triangularis (Bergen & de Kaenel in Bergen et al., 2017) n. comb.
Pl. 4, figs 25, 26
1971 Sphenolithus ciperoensis Bramlette & Wilcoxon,
1967 – Roth et al.: pl. 3, figs 4, 9.

67

1990 Sphenolithus cf. S. ciperoensis Bramlette & Wilcoxon, 1967 – Okada, pl. 2, figs 3, 4.
2014 Sphenolithus sp. H Aubry: pp. 328, 329, 334.
2017 Sphenolithus triangularis Bergen & de Kaenel inBergen et al.: p. 97, pl. 10, figs 15–24.
Basionym: Sphenolithus triangularis Bergen & de Kaenel
in Bergen et al., 2017, p. 97, pl. 10, figs 15–24. Bergen,J., de Kaenel, E., Blair, S., Boesiger, T. & Browning, E.
2017. Oligocene–Pliocene taxonomy and stratigraphy of
the genus Sphenolithus in the circum North Atlantic Basin: Gulf of Mexico and ODP Leg 154. Journal of Nannoplankton Research, 37(2–3): 77–112. Diagnosis: A small
furcatolith with a low bifid spine, and a proximal element
cycle that is ~60% of the total height. The angle between
the median axis and the top of the proximal element cycle
is approximately 45°. The base of the proximal element
cycle is strongly concave. Thin distal extensions of the bifid spine may or may not be present, and if present, canvary greatly in length. The total height and the basal widthof the proximal cycle are approximately equal, such thatthe peripheral outline approximates an equilateral triangle.
Remarks: This small species was probably overlooked inmany earlier studies, where it may have been considered asmall, low form of S. ciperoensis.
Furcatolithus avis (Aljahdali et al., 2015) n. comb.
Pl. 4, figs 27, 28
2015 Sphenolithus avis Aljahdali et al.: p. 193, pl. 1, figs
1–5.
Basionym: Sphenolithus avis Aljahdali et al., 2015, p.
193, pl. 1, figs 1a–d, 2a–d, 3a–d, 4a–f, 5a, b. Aljahdali, M.,
Wise, S.W. Jr., Bergen, J. & Pospichal, J.J. 2015. A new
biostratigraphically significant Late Oligocene Sphenolithus species from the equatorial region. Micropaleontology, 61(3): 193–197. Diagnosis: A small to medium-sized
furcatolith with a very low bifid spine, and a proximal element cycle that is ~70% of the total height. The elementsof the proximal cycle are curved in lateral view, such thatthe base of the proximal cycle is strongly concave. The
angle between the median axis and the top of the proximal
element cycle is approximately 40°. Thin distal extensionsof the bifid spine may or may not be present, and if present,
can vary greatly in length. The total height and basal width

68

Howe

Plate 1
1, 2: Diantholitha; 3–18: S. primus Group; 19, 20: S. anarrhopus Group;
21–26: S.radians Group; 27–30: S. kempii GroupUltrastructure and taxonomy of the Sphenolithaceae

69

Plate 2
1–10: S. kempii Group; 11–28: S. dissimilis Group; 29, 30: S. conicus Group

70

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Plate 3
1–12: S. conicus Group; 13–28: S. delphix GroupUltrastructure and taxonomy of the Sphenolithaceae

Plate 4
1–20: F. predistentus Group; 21–24: F. ciperoensis Group;
25–30: F. triangularis Group

71

72

Howe

of the proximal cycle are approximately equal, such thatthe peripheral outline approximates an equilateral triangle.
Remarks: This species is clearly intermediate between F.
triangularis and F. umbrellus, having the small bifid spineof F. triangularis, and a high proximal cycle with curved
elements, similar to that of F. umbrellus.

Furcatolithus umbrellus (Bukry, 1971b) n. comb.
Pl. 4, figs 29, 30
1971b Catinaster? umbrellus Bukry: p. 50, pl. 3, figs 10–13.
1986 Sphenolithus umbrellus (Bukry, 1971b) Aubry &Knüttel in Knüttel: p. 279, pl. 5, figs 1, 2, 5–10.
Basionym: Catinaster? umbrellus Bukry, 1971b, p. 50, pl.
3, figs 10–13. Bukry, D. 1971b. Discoaster evolutionary
trends. Micropaleontology, 17(1): 43–52. Diagnosis: A
large to very large furcatolith with a greatly reduced vestigial bifid spine, or no bifid spine. The proximal element
cycle is >95% of the total height. The proximal cycle elements are curved, so that the base of the proximal element
cycle is strongly concave. Remarks: This species is thelast representative of the genus before its extinction in the
Early Miocene. The SEM photographs of Knüttel (1986,
pl. 5, figs 1, 2) show some specimens of F. umbrellus withtiny elements just above the top of the proximal cycle,
which may be the vestigial elements of a bifid spine.

is absent in some species, has been shown to be key tounderstanding the evolution of Furcatolithus from Sphenolithus. When examining species with a bifid spine undercross-polarised light, particular attention must be paid tothe orientation of the median suture of the spine relative
to the microscope slide because the birefringence of thespine changes greatly between orientations where the median suture is parallel or orthogonal to the slide.
Acknowledgements
Many thanks to Dr Jeremy Young, who encouraged me to follow up on my initial observations on the lateral element cycles
of Sphenolithus. His advice and insights throughout the writing of this paper were invaluable, although any errors are minealone. Jeremy astutely made the observation that S. compactus
is a senior synonym of S. paratintinnabulum. My colleague Dr
Dave Bord was very helpful in discussing and refining the concepts in this paper. I am very grateful to Drs Jean Self-Trail andJim Bergen, who provided invaluable advice on the manuscript
before submission. The reviews of Drs Denise Kulhanek andTom Dunkley Jones were much appreciated and improved themanuscript substantially. Thanks also to Dr Daniel Peyrot of the
School of Earth and Environment at the University of Western
Australia for providing me with access to the research facilities
and equipment.

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